About how many days until my cat gives birth?

by shelby :3
(USA)

My cat (who we keep strictly indoors and were planning on getting spayed in May) was accidentally let outside by my boyfriend on his way to work and he would have been late if he went to put her back in, so she was outside for a very short period. This was in late March/early April, not sure, which means her due date could be anywhere from today, to June 8th.

I want to be present during her birth in case of complications so I want to know what day people think is most likely. I have been able to feel movement for a week, especially the past 3 days, she is very very clingy and never leaves my side, but hasn't shown any obvious labor signs apart from making a "nest."