Before the reels turn, and after the last win
Each spin lands on fresh reels, so the timing of the bonus round is not known in advance. Nobody can say how often Free Spins will start, and one session of Bigger Bass Splash ends with a result that is random, whatever the RTP. The RTP figure describes the return over a very long run, not the outcome of your evening.
Every spin on the reels follows one RTP version, and only the game rules show which version is running. Read the rules inside the game before you play, because a figure quoted elsewhere may describe another version. Two versions can pay out differently over time even when the reels look the same.
Each spin on the reels can in principle reach the top of the pay scale, but the maximum win of Bigger Bass Splash is a ceiling reached very rarely. Treat it as the limit of the game, not as a target. No one can predict which spin, if any, will get there.