Yes you need to make a timer, and make the while loop continuusly check it, and if it reaches the time you desire to restart and spawn.

Do you even know what your code in post 1 does, exactly?

The only reason I replied is because this for loop does not do what you think it does:
first, i is initialized to 0. Then, each time the guard is executed (i <= random(2,30)) a new random number is generated. So it makes sense that this loop only executes about 5 times.

This question is the somewhat more advanced version of "I know 5 * 5 = 25, what should 6 * 5 be?" please, please try the example games from the bgt manual, those are very well commented and will teach you what's going on. If you don't understand those, read the language tutorial. If you don't understand the language tutorial, although this might be harsh, stop programming.

I also find it odd how someone who seemingly doesn't even understand the basics of timers is supposedly making a game with enemies and stuff. Things don't quite add up here. Know what I'm saying?