Water Pump Job Question

Hey guys, I'm replacing my water pump this weekend. I'll be working in the parking lot (we LOVE apartment living) and some thunderstorms are due to roll in this afternoon.

I would kind of like to get started this morning it case it takes me longer than a day (because I'm really an amateur here and sometimes dumb things take me a real long time) but I'm wondering if I get partially through (ie I get it off but I don't have the new one on yet) will leaving the car outside like that overnight in the rain hurt anything? I would of course close the hood. I have considered I could tape some plastic wrap or something over the mating surface for the water pump so bugs or whatever can't go into the block.

Anything else I need to consider here? If this is a terrible idea, I may wait until tomorrow and start at the ass crack of dawn tomorrow.

Wish I had a garage LOL. Hopefully someday.