Can anyone tell when the bonus comes?
Choosing a bet before your first spin means accepting that nobody can say when the bonus round will come. Free Spins start when two or more Scatter symbols land on reels 2 to 5, and no one can predict that moment. The result of one session is random whatever the RTP, so a high RTP describes the long run, not the session in front of you.
Deciding whether to trust an RTP figure starts with the game rules. The RTP figures listed for Zombie Carnival describe the game itself, but only the game rules show which version Betbolt Casino runs. Open them before you stake real money, and find the version named there.
Chasing the top prize means understanding what the maximum win really is. It is a ceiling, and it is reached very rarely. Because it is stated as a multiple of your bet, a bigger stake raises the money involved. Size your bet to what you can afford to lose.