Time Travelling Tips
This entire situation is very complicated to sort out (hence this excessively long section), but I will do my best in explaining it. Time travelling back and forth between the Past, Present and Futures whenever you want, using relatively easy to access time travel points, is usually not beyond achievement in other levels, and I have based my previous explanations on the ability to do this, so you can choose where you want to go at any particular point. This zone, however, is designed in a very complicated manner, with lots of routes that are closed off from each other, and there are worlds of differences between their exact structures across the timezones. Furthermore, it all takes place entirely within the first half of the zone, as the moment you begin to explore the long, winding route of the second half, you've gone too far and will find that backtracking is difficult. In fact, it's only possible at the very end of the zone, as explained in Point #4. Essentially, if you want to go into the Past, find the machine, then travel to the lovely Good Future successfully, you'll need to pretty much follow step-by-step instructions, as they're very hard to figure out by yourself because of many areas that deny backtracking at certain points, and limited time travel opportunities. My research also suggests that Mega CD users are at a slight disadvantage compared to Sonic Gems Collection and PC users of the game. In the MCD version (though possibly just the emulated version of it, I cannot yet confirm), it doesn't even seem to be possible to get all the way through the zone in the Past without having to return to the Present (see Point #1). Let me say that without assistance, this will probably be your toughest time travelling challenge, but luckily, you have me and my wonderful guide to help you..
Firstly, in terms of time travel opportunities, things are very similar to the situation in Zone 1, in that there are only a couple of fool-proof places to time travel using two opposing horizontal springs, but this time you can also use a zone-exclusive object to your advantage. These are the rotating wheels suspended in the air, mostly found in a tall open room right at the start. If you land on the top half of one of these wheels, Sonic will start to run around its circumference, preferably if you leave the left or right buttons alone, otherwise he tends to fall off. Instead, press down once and Sonic will spin in a ball with increasing speed as he goes round and round, and this is perfect for when you've got a warp activated. Otherwise, if you jump off with your speed increased at the right time, you should be able to gain more height upwards. Using these for time travel is not necessary, but it is an option open to you.
Now, the step-by-step guide to time travelling and Good Future-earning in Zone 2.. Starting from the beginning in the Present, you'll proceed upwards into the tall room filled with rotating wheels and various platforms etc. This room continues off to the right at a couple of exits on the way up, but what you want to do is use the techniques described above to ascend to the very top route, using the spinning wheels to propel you. A short way along this top route as it begins to the right, you'll find a pair of horizontal springs and a Past post to go with them, so you should have no trouble there. There is a Future post on the way up through this initial room, and I suppose you could accidentally activate it using the wheels, but in the Futures, you can easily use the same mechanisms to return to the Present, at this point. All being well though, you'll arrive in the Past, and you'll find there are no horizontal springs at the same point, and you cannot return to the tall room because a high ledge on the left prevents it. Go to the right and press the button to open up the hatch into the transportation tubing network. When you arrive at the four-way junction, press left to be taken to the bottom route. When you reach the exit hatch, you need to drop down to the area below on the right but be careful, as there's a small gap in the floor that you're going to land on, and if you fall through it, you'll miss your opportunity at the machine. Try and drop close to the wall, so that you land by a Future post. Leap over the gap and go to the right to find a slow moving crushing block, and the machine is in a room just above this.
Ok, so the machine is destroyed, but this is where things get really complicated. For me anyway, as I've got to explain it all to you. If you're playing the Sonic Gems Collection or PC version of Sonic CD, you can either continue to frolic in the Past for the remainder of the zone, or you can return to the Present, and there's a slightly less than fool-proof opportunity to do this very soon after the machine. If, however, you are playing the original, Mega CD version of the game, it seems you will be unable to complete the zone in the Past (see Point #1 to find out why), and will have to return to the Present, but only via a time travelling opportunity that appears later in the zone. It's also worth noting that a much easier alternative option exists if you've got plenty of lives to throw around and won't mind sacrificing one by topping yourself. This will allow you to go straight to the start of Zone 2 Past where you can use the spinning wheels to time warp into the Present, and then from the Present, you can use the options available in that area to head on into the Good Future, as the destruction of the machine is saved, even though you lost a life. Bear in mind of course that Zone 3 is hard as nails, so you might need all the lives you can get for it! If you'd rather play it safe and honest, continue reading, as there are long ways around the problem.
For Gems and PC users only, ensure that you've touched that Future post on the left side of the gap I told you not to drop down to, near the machine, and then.. drop down it. Down a short slope, you'll find a long stretch of open floor. There's a spring on a wheel at the very end of it, but it's just long enough for you to run right across it, obtaining your required three seconds for time warping, if you start from the slope and you DON'T use a peel-out or spin dash this time, as these are too quick for this amount of space. Just pick up speed as quickly as you can while running normally and you'll probably need to jump over the spring at the end - should be just enough room. If you're on the Mega CD, or if you tried that time warp and failed, you can continue on to the next, slightly hidden opportunity that is pretty much a guaranteed success. To get there, head onwards, into a straight section of shutters. Use the revolving device to go behind the shutters and run to the far right end. You'll fall through an invisible collapsing floor to another shutter area below, and you can continue the zone from here. Eventually, you'll reach the area explained in Point #1, with the diagonal spring that lacks enough power in the Mega CD version. Use it, or the moving spring below it, to enter the in-built ledge on the left-hand wall, below the highest ledge, and this consists of a transport tubing entrance that takes you to the second four-way junction in the zone. You'll come in from the right side, and should choose to go down at the junction, which delivers you to a large, but ultimately dead-end area further back. Use the first long moving spring/crusher thing you come across to ascend to the ledge on the upper left. Carry on left, then drop down below and just to the right, you'll find a sight for sore eyes; a lovely pair of horizontal springs and a Future post between them. Get your ass to the Present, pronto.
Right, so now you've destroyed the machine, and returned to the Present. You can now complete the zone as normal, but you don't want to do that, do you? You want to take a gander at the Good Future, don't you? That's the spirit, and it's still possible, regardless of which of the two time travelling methods you took, described in the previous paragraph. The area with two opposing springs is actually still there in the Present (and Futures for that matter), but you can't really use it, and here's why: it's got both a Future post AND a Past post in between the springs. Obviously, you have to touch them both and you'll come in running into them, so whichever one you touch second is the one you're stuck with. In my tests, the second one you touch as you appear into the Present often seems to be the Past, unfortunately - the one time we DON'T need it! If it happens to be the Future for you though, then you've struck very lucky indeed, and can safely time travel away between the two springs, and there's also a ten ring box there too, so you could get caught in front of that, then have your choice of posts (remember to get the one you don't want first, then the one you do). Otherwise though, you'll need to get out of the area and continue your quest, as there are no other posts in the vicinity that will allow you to return to these springs. Unfortunately, if you took the alternative time travel method listed above by running across the straight ground just after the machine, these springs are also useless to you because you've appeared on the lowest route. Right above you, the route splits into a higher one that allows access to the area with the springs, but unfortunately, it's too high to reach from where you are now.
There are two other solutions you can use to time travel from the Present into the Good Future, one of them much longer but less risky, and the other is on the way to the end of the zone, but you might mess it up, and then be unable to backtrack. Regardless of where you've appeared coming from the Past, just continue right until you reach the Present equivalent of Point #1, which now contains handy conveyor belts. If you want to take the longer, but safer method of time travelling, use the conveyor belts to get inside the small room on the left-hand wall, below the highest ledge. In here is the entrance into the tubing network, and at the junction, choose the up option first to grab yourself a Future post in a dead end room up top, then return to the tubing junction and go left. This will take you to the top route, where you can backtrack all the way across the shutter area and platforms to once again find the first pair of horizontal springs, way back near the beginning of the zone. The other option is to continue the zone as normal by carrying on up the highest ledge, rather than going through the transport tubing, and there's a Future post for you on the way. Tread gingerly once you begin to head downwards via a couple of long ledges on alternating sides. Look out for a large spinning wheel object just to your left that's below a couple of small stationary platforms. Do not fall because you won't get a chance to go on the wheel from below it, but carefully leap up onto one of the small platforms and drop onto the wheel from the space between them, then use it to create a time warp by pressing the down button. If you really want to go to the Good Future, I advise the first method. If you're not all that concerned about it, you may as well attempt the second.