You don’t modify the timer. It like a stop watch - it can only be started, reset, paused and unpaused. You can’t change the stopwatch time though.
Instead you change the value you check the timer against. You’ve hardcoded the 90 seconds. Use a variable for this instead:
Also, reset the timer when you pause it, otherwise it’ll remain over 90 and the timer check events will continually execute.
And get rid of that trigger once - you’ve only had to put it in there because the timer wasn’t reset when it was paused.