da if you're doing least common denominators, your best bet would probably be to do it at minimum 30seconds for 3 pts, which would be 30sec/point

3 pts: 90 seconds or 1.5 minutes
4 pts: 120 seconds or 2 minutes
5 pts: 150 seconds or 2.5 minutes

if you want people to reach for the 5 pts without going over 150, you can make it 140 or 145 seconds to get the 5 pts to make anons want to get 5 pts while doing less than 30 seconds to get to the 5 pts tier from 4 pts