random powerups

Harman14

I was working on a endless runner game and i was trying to make the powerups spawn at random times but to decrease frequency as the game progresses, ive tried to set up 3 rules for 0-30secs in the game 30-60secs and 60-infinite secs and have the do as a timer set for after random secs spawn actor.... didn't work at all. I'd really appreciate if someone could help me out with this.