As long as the babies are moving around I think you are ok. It's Sunday now so one more day is ok. Just get the vet tomorrow and have him check her out to make sure everything is alright. I guess just like humans sometimes they can go over their due day. My RB Mytsi went 74 days with her last litter and everything was fine. But do call the vet tomorrow and have he checked. Better safe than sorry.

One question...are you planning on having her spayed once she weens the kittens at 8 weeks? There may be some things you don't know about a cat going into heat and pregnancies. Everytime a cat has a heat and everytime she gets pregnant it increases her chance of getting certain cancers. I did not know this myself until my RB Mytsi was diagnosed with Mammory cancer. I lost her to the disease after 5 months. We had surgery to remove the cancer but it came back very aggressively and claimed her life. Please, consider having your cat spayed once she weens her kittens.