
The temperature will fluctuate, down and back up again, during the final stages of a pregnancy but it's when it drops and stays down, that you can usually expect labour to start within 48 hours. I don't set too much importance on the temperature however but on the number of days from the first mating (I do know that conception may not take place immediately). I'm assuming you know who the sire is because if he's significantly bigger than your 'toy bitch', she may have difficulty whelping naturally, and need a C.Section. In any case I didn't let mine (not a toy breed) go over by more than two days without involving my vet, or, once labour starts (strong contractions, pushing hard), for no longer than about 1 hour without seeing a puppy delivered - each delivery. If she's going to need a C.Section, it's way better to get her in for one before she becomes exhausted, risking her life and those of the unborn puppies.
I hope you have a mentor to hold your hand if this is your first pregnant bitch.