Look up the version before you spin
Decide how much you will spend before the first spin, because the bonus round cannot be timed. Nobody can say how often the free spins will land in Sweet Bonanza, and no sign on the grid predicts them. The result of one session is random, whatever the RTP. A return figure describes long-run averages, not the evening you are about to play.
Look up the RTP version in the game rules before you spin, because the version Bigwin Casino runs is shown only there. The versions of Sweet Bonanza differ by a small margin, so the rules are the only place to confirm which one you are playing. Read that line before you decide how long to play.
Treat the maximum win in Sweet Bonanza as a ceiling that very few sessions reach, not as a number to plan around. Set your stake so that a run of ordinary results still fits inside your budget. Whether a given session comes near that ceiling is decided by chance, and no amount of study changes it.