It seems to depend on the cat;the more experienced mothers taking less time and giving less obvious notice; but none give you much notice.I had one that left our new home, went back to our old home in the village, which we'd just sold, went in, went upstairs, found our old bedroom and produced the litter on the new owners' bed!That was all, evidently, premeditated. That said, she could have done all this within 45 minutes.