Will the Free Spins arrive on the next spin?
Deciding how long to play starts with one question: when will the bonus come? Nobody can tell in advance how often the Free Spins or the Money Respin will start. The result of one session is random whatever the RTP, because the RTP describes the average over a very large number of spins, not the next one.
Checking the RTP before you stake means opening the game rules, because the RTP version in use is shown only there. Pyramid King has one RTP version, and the table on this page converts it into money for each A$100 staked.
Choosing a bet size means weighing the top prize as a ceiling, not as a likely outcome. The maximum win of Pyramid King is set as a multiple of the stake, and a result at that ceiling is reached very rarely. Size the bet to what you can afford to lose.