How often will the free spins come?
Deciding how long to play Mahjong Ways 2 means accepting that you cannot time the bonus round. The free spins come at random, so no one knows in advance how often they will land. The result of one session is random too, whatever the RTP of the version you play.
Checking the version comes before the first spin. Which RTP version runs on this site is shown only in the game rules, so open them before you stake any money. An RTP figure only describes the version it belongs to, so match the two first.
Weighing the maximum win means treating it as a ceiling, not an expectation. The maximum win of Mahjong Ways 2 is reached very rarely. Set your stake from your budget, not from the top figure in the table.