Bricks, Masonry, Asphalt and Concrete - Ok to pour in the rain?

I'm scheduled to pour 10yds on friday morning, 40 footings and a slab that will tie the footing together. The thing is there's a good chance it's going to rain, though they're not calling for it to be heavy and mostly withing a 2hr window (of course in the morning when I'll be pouring the concrete.

How much rain is too much rain when doing this type of work? If rain is in the forecast after I pour and finish, should I cover everything with a tarp, or just leave it exposed?

Well it didn't rain, and I ended up needing 13yds. One of the most physically demanding jobs I've ever done, but it should last a long time (3/4 5000psi).