[TimT]

Water is concretes best friend and biggest enemy.

If your contractor had a 4 hour window when it didn't rain, you might actually get a better product. If he was able to screed and finish the concrete during the no rain window, and the concrete hydrated to initial set, rain would be like manna from heaven.

Any extra water would be considered curing water.. Curing of Bridge decks usually involves over 7 days of continuous wetting.

If the rain got mixed into the finishing operation, i.e. changing the water/cement ratio you may have problems with scaling etc. Most problems will be finish problems that will manifest in years... the underlying concrete should be fine (depending on the slump the contractor mixed the concrete to).