perlpal,
The obvious problem has already been pointed out to you, but there are some additional things you might want to consider. For instance, if $_time_offset is a negative number, you still introduce an infinite loop. Additionally, you have no sleep before the next iteration of your loop. If execute_attack() doesn't do as you expect, this could turn into a runaway CPU hog. On the other hand, if execute_attack() itself becomes a long running process - you still may run longer than you want - see alarm and %SIG in perlvar for a potential solution.

You should be able to take the ideas I am providing and build on them. If you don't understand or come up short, come back and ask for more help - but keep in mind that with a sub name like execute_attack(), we will likely want a better explanation of what your code is doing before helping further.