You set the condition,
Then if you want them to spawn every 5 minutes, do this.
Wait 300000 milliseconds.
Create 10 Zerg _____ at location for player X.
Preserve Trigger.
I didn't go into Death counters to replace waits since i assume those are not suitable for your level yet.
Edit:

Meh.. i posted at the same time ChoasRyder did - some info are repetitive.
Re-Edit: Since my post is too similar to the one above, I'll just go into death counter to replace waits.
Firstly, make Hyper Triggers like this:
Starcraft checks triggers every 2 seconds or at intervals which there are waits. Therefore first add a trigger like this for a player without any waits.
-Always
~Wait 0 milliseconds.
~Wait 0 milliseconds.
~Wait 0 milliseconds.
~Wait 0 milliseconds.
~Wait 0 milliseconds.
... and so on until you reach 63, then add Preserve Trigger.
Then copy the trigger 3 times.
By doing this, starcraft will check trigger 12.2 times a minute.
Why use death counters?
Waits in your triggers causes a blockage for other triggers to fire. They stack up and some triggers don't run until the wait has finished. Therefore to infiltrate this from happening, we use death counters.
Death Counters are just a method of calculating time using the nature of Starcraft's triggering checking speed and then setting something to happen, you can set/add/subtract deaths directly using the trigger SetDeaths. Then what you do is, you make a trigger like this.
-Always
~Add 1 deaths for Independent Starport (or any unit that don't exist in the game) for Player X.
~Preserve Trigger.
This causes starcraft to continously add deaths to 'Independent Starport' owned by Player X. However, it will not automatically go to infinite, instead as I have mentioned before... with Hyper triggers, Starcraft check triggers 12.2 times a second. So it adds around 12 deaths per second. Using this method - you are able to estimate how many deaths will be added in 3 minutes. (3x60x12.2 = You can work it out yourself

)
After it have obtained that amount of deaths, run an action that creates 10 zerglings at the location.
(After reading ChaosRyder's post, assuming you are not creating units reptitively, I don't think i need to mention how to cycle the death counter)