A game cycle is how the Gambling Commission defines one unit of play on an online slot: from the stake being placed to the result being shown. Since 31 October 2021, a GB-licensed online slot must take at least 2.5 seconds per game cycle.
The rule caps the pace of play. At 2.5 seconds, a game cannot exceed 1,440 cycles an hour, which in turn caps how much can be staked per hour. Illustrative example: at £1 a spin, the most that can go through a game in an hour is £1,440, and at 96% RTP the expected loss on that would be £57.60.
The same 2021 rules banned turbo spin, slam stops and autoplay, all of which sped up play. Stake limits also apply per game cycle, with extra stakes inside a feature counting towards them. See game design rules.