Just to add a little clarity:
There is a perfunctory security check to enter the terminal. They look at your passport to ensure it is you. You run your bags through a large x-ray machine and walk through a metal detector that seems to be set to almost never go off.
You then check-in with the airline.
For non Philippine residents, you no longer have to complete a departure form.
Stop at the booth and pay the 550-peso departure tax (starting next month, it will be included in the ticket price).
When ttuna3 refers to "customs" he/she actually means emmigration (passport) control. There is no customs check for departing passengers.
You then go through passport control.
After passport control is the airside security check, which is now like most airports in the world.
That's it.
Terminal 1, where OZ still departs from, is an armpit of armpits. Most carriers are moving to T3, but I haven't heard of OZ doing so.
The lounges in T1 are as bad as the terminal. Other than a place to sit and something to drink, they are nothing to miss.
I would try to arrive at the airport about 1:30 before my flight, but beware that Manila traffic can be heavy and unpredictable, particularly if it is raining. The time of night you are leaving shouldn't be a major issue.
At least that's how it was two-days ago when I left.