1st, if this is for Construct Classic (and not C2), it should be moved into Help.
Secondly, I would recommend using the clamp(a,b,c) system function for timers instead, as it is much more reliable.
have a private variable "timer"
"timer" greater than 0
set "timer" to Clamp("timer" - 100 * TimeDelta, 0, 500)
[The "500" corresponding with 5 seconds, 300 with 3, etc. I've been told that having things in multiples of 100 is easier and better in the long run, as calculations with values less than 100s can be buggy.]]
"timer" = 0
sprite : create bullet
sprite : set "timer" to [insert number here]