Here it's uncommon to mail invitations and too impersonal to leave a card at someone's house without announcing yourself. You are supposed to see people face to face and invite them and give them the details (time of party often optional or left quite vague). The exception would be recieving wedding invitations from absolute strangers who happen to live in your neighborhood and are obligated to invite you (yet still expect you to come. They will actually cook for one thousand people without any RSVP). I'd say the majority of our invites from friends have been made on the day of the party and only sometimes the day before. One local friend here explained it as a test of friendship. People want to see your loyalty... If you'll drop whatever to be there for them.
Well, I can't quite shake my American-ness sometimes. I want my daughter's friends to show up! I have a hard time trusting their system :) I figure kids have less say about these things, so I at least want to invite them early enough so the parents won't "balik kampung" (go back to their hometowns) and miss the party. But I couldn't help but laugh when each time we invited a kid, they asked, "malam ni?" (Tonight?) even after I said "Sunday" like 3 times. They are so used to being invited the day of, I hope they can keep it In their brains. Haha.