Bonus timing and single-session outcomes
Each spin lands a new set of symbols on the five reels, and the bonus rock can appear on any of them. How often three or more rocks arrive and start the Mega Hold and Spin feature is not known in advance. One session's result is random, whatever the RTP of 96.64 says about the long run.
When the reels stop, each result follows the RTP version the game runs, and that version is shown only in the game rules. The table on this page gives the RTP in money for A$100 staked, so you can read the rules and the table side by side.
Big rocks and chest awards can lift a round sharply, yet the maximum win is a ceiling reached very rarely. It is a multiple of the bet, so the money it means grows with the bet size. Plan each session around the bet and the time you want to play, not around the top prize.