Simply run past a “Future” or “Past” time post and find a place where you can gain a lot of speed (loops or springs that go back and forth). This will cause sparkles of light to form around Sonic. Once Sonic disappears that means you have traveled through time. If you get stopped by something and the sign post to the left of your life count is blinking that means that you are about to lose the ability to time travel. This will pop up during the time travel sequence. NOTE: Technically this achievement is missable but I’d find it hard to miss unless you deliberately do so.