When will my cat give birth?

1: she will be spayed as soon as her kittens are weaned, she was a stray and pregnant when I got her.

We don't know exactly how far along she is but she has been noticeably pregnant for 3 weeks and I suspected around Christmas because she pulled the fur from her nipples.

For the last 3 days she has been searching for a nest, grooming excessively, eating less, and being less tolerant of our other cat. And just today she had an off-white discharge I think was her mucus plug and her nipples look full. Some articles I have read say she should have them in the next 24 hours and others say it could be a week.