From what I’ve read in the past, it can be hard to confirm pregnancy in a rabbit other the X-ray/sonogram. There is only a small window of opportunity to feel them and that’s about 2weeks in. Experienced breeders probably can though.
As to when they are ready to birth; fur pulling and nest building can happen right the day before -sometimes not at all. It’s a hormonal change that allows the fur to become loosened and pulled easily.
I’ve only had 1st hand exp one time, back in 2012. My rabbit Maple seemed to become very industrious on a Friday night. Just had a very alert look about her. Nothing happened though until the Sunday night.
She apparently did pull fur earlier on the pregnancy but she wasnt with me at the time. I do wonder if it was due to some stress as she was being rehomed by her former owner.
Up until that weekend, it was only a suspicion that she could be pregnant. I didn’t have the benefit of knowing her nature beforehand. She was a very scared and vocal little rabbit when I met her. That changed immediately after she had the litter.
I had also read expecting mums will go off their food before giving birth. So don’t be surprised if you see your girl do that the day before.
If it’s a false pregnancy, she will probably still pull fur/nest, although that more likely to have happened earlier on.