Unfortunately, current CPC emulators don't have a rewind feature like in games such as "Prince of Persia: Sands of Time" or "Braid" for PCs.
A very simple approach is to make an a SNA for each frame and limit the RAM snapshot to 128KB, which is ok for 99% of CPC software. 128KB * 50 frames * 60 seconds = 384MB needed for the rewind functionality.
Users can stop rewinding whenever they want. They just have to press and hold a rewind button to play the game backward at 1x speed. When released, time goes forward again.