Re: how long can they be showing labor signs? Quite a long time! A couple of days to a week- I've had cats do that squat and push thing for a few days before they actually give birth- you start to wonder if they aren't holding them in.
Assuming they are here but if not- have you read up on what to do in emergancies? Like how to tie off an umbilical cord or pull out a stillborn, etc? Hopefully not necessary. Last spring my friend and i rescued a cat and 4 newborns that were about 24 hours old. 3 died within a few hours of trying to warm and feed them (she had been unable to nurse because they were tangled in weeds). Then, a few hours after trapping her and putting her with her babies - after 3 hours was one baby- she tried to give birth again and then again the next day was having contractions. My friend had to pull out a dead kitten very gingerly and bury it with the others. This was a tortie mom who was so traumatized that she had no "torti-tude". She is partially blind as well. mom and one kitten (no longer a little kitten are doing well and seem to be "keepers"!!