I'd let it completely dry out, which may take a while, and then look at the plaster. If it been wet too long it will have made the plaster soft, in which case it will need removing down to sound material. If you are lucky and the plaster is sound and hard then I would give it a coat of stain block before re-painting. I usually paint the whole wall with the stain block rather than just the patch as it can sometimes show through the paint finish as a patch.

I'm not sure that chipping the plaster away will speed up the drying process much, but clearing away all the lose dust and debris and making sure there is a good air flow round the patch definitely will.

If you have access to a voltmeter, (a very cheap simple one will do), set it on ohms and stick the pins in the wall. You should get infinite resistance, try it on a dry wall if in doubt.
If you get a voltmeter now you can monitor the wall and see how the resistance increases as the wall dries out. Once you get to a more or less infinite reading you are set to go.

Cheaper option to test the wall is to seal some clear cling film or polythene up against the wall overnight, if you have no condensation behind it then the wall has normally dried out.