If you want to add platies, wait until the tank's fully cycled. A week's not long to wait at all. Don't add a pair though - either get a trio (1 male, 2 females) or stick with 2-4 of only one sex (males stay smaller BTW and females may come in pregnant as they can store sperm for months). If you get a male/female pair, the male will chase and harass the female constantly, trying to mate with her, and that'll stress her out. Check the livebearer section out for info. on sexing them if you don't know about that already. It's very easy.
Also, I should add, that if you plan to keep more than that one angel in your tank, you should add the other before this angel becomes sexualy mature and becomes territorial or you'll have trouble with itnroductions later on (but that can wait a week or two as well!).
