Ok My Hairless Rat Is Pregnant When Will She Give Birth??

Question

I didn´t see when she got pregnant because I left her with the male about 2 weeks. I noticed yesterday that she was getting fat and big, also her nipples are bigger like if they were swollen. Some people told me you could guess when will she give birth because of the nipple thing.

Also can you tell me what is the average time a rat is pregnant before giving birth??

I know what I will do with all the babies, they will be in a nice home where people will take care of them. I know that sometimes hairless rats won´t make good mothers and I am willing to hand feed the babies.