I made a respawn trigger for like normal mops in WoW or any MMO or game that has mob respawn timers.. Maybe you can use it for your map. If you kill 5 of them then each mob respawns like 10 secs later they dont ALL spawn.. 1 Spawns every 10 seconds.. so if you kill 5. You would have to wait 50 secs for all 5 mobs to respawn... I was trying to make a timer Array and have each mob its own timer, but I couldnt quite figure it out.. so i simplified it.. here is the Code as text. You need a global to track how many mobs died if you only want to have 5 mobs on screen at a time.. That variable is just to say when to stop.
Unit - Any Unit dies
((Triggering unit) is in Test) == true
(Owner of (Triggering unit)) == 15
Variable - Modify UnitsDead: + 1
** Test is the Test Region I made to test this trigger out. You can set the Region to Entire World if you want**
Timer - Every 5.0 seconds of Game Time
General - If (Conditions) then do (Actions) else do (Actions)
UnitsDead > 0
Unit - Create 1 Zergling for player 15 at (Random point in Test) using default facing (No Options)
Variable - Modify UnitsDead: - 1
Hope this helps.