Dumb AOS Trigger Question

I've got one of those stupid AOS questions. I figured out how to spawn units, but I want more units to spawn after so much time. I want 3 footman to spawn for the first 30 min, 3 footman and a rifle for the next 30 min, 3 footman and 2 rifles for the next 30 minutes, and 3 footman, 3 rifles, and a catapult the next 30 minutes. How can I make it so different units spawn after so many minutes of game time?

I don't see why Game Time wouldn't work...

E - Time - Elapsed Game Time is 1800 seconds
A - (Your new spawn stuff here)

Turn on/off the triggers with another one with time elapsed=30mins, turn off 1, turn on 2, wait 30 mins, turn off 2, turn on 1 etc.

Couldn't you use a variable to do this? Something like this.
If your respawn time was like 30 seconds here how it would go.

Events - Every 30 Seconds of Game Time
Conditions - None
Actions - If Then Else (Mult Statement)
Condition - TimeSpawnUnit = 60
Events - Turn off this trigger
Turn on Trigger B ( just like this one except different units )
Set Varaible TimeSpawnUnit = 0
Skip Remaining Actions

( End of If than Else )
Spawn 02 footman for player X at X region.
Set Variable TimeSpawnUnit = TimeSpawnUnit + 1


Trigger B would be the same except for different units.
Hope that helps
I'll explain just incase you don't understand
When TimeSpawnUnit is equal to 60, the trigger has run 60 times. 30 seconds times 60 is 1800 seconds, which is erm...30 minutes!
So when that trigger has run 60 times, it turns it self off and turns another trigger one, which should be the same thing except for other units at the bottom below IF than else.