Question

If something has a 0.35% chance to occur every 5 minutes how long will it take for it to be guaranteed

Answer 1

It will never be guaranteed.

Explanation:

Chance cannot be added, and chance will remain at 0.35% forever

Answer 2

Never

Explanation:

After 5 minutes the chance is .35%

After 10 minutes the chance remains .35%

You can't add chances, like flipping a coin, the chance is not dependent of the previous outcome, just because you got heads the first time doesn't mean you'll get tails the second time even.