There is only one timer in FPSC and every time the command "timerstart" is used in a script it is restarted. So, it could be very volatile to use.
However, if you want to try, you need to have in a script when the game starts
:state-0:timerstart,state=1
:state=1,timergreater=(whatever time):state=10
:state=10:(whatever you want to happen
However, the timer could restart for a variety of reasons and you may never get to the time you want the event to happen.
Use of a mod that has individual entity timers would more than likely work for you.
Addendum:
However, I am sure there is a work around for this. Where you need to search is in the "scripts" forum, not this one and this actually belongs in the scripts forum. You might want to search using "multiple timers" or something like that. Conjured Entertainment has a way of having more than one timer.
-----------------------------------------------
OliveTreeGames