Once their temperature drops they usually go into labor within 24 to 48 hours.
You said the pups will be tiny, so I'm assuming mom is a toy or very small breed? Have you done x-rays, to see how many she is carrying? If she is carrying a singleton, they tend to be larger than pups in a multiple pup litter, which can be problematic, and require a c-section regardless.
Do you have a mentor who can help you with the whelping? Having someone experienced who can either be there in person or just a phone call away is helpful.
Do you have plans in place in case she winds up needing a c-section? having a vet lined up beforehand, just in case, is always a good idea.
If you have any suspicion that something is wrong, contact your vet immediately, and be prepared to take her in for a c-section. It's far better to show up at the vet clinic with a healthy litter not needing a c-section than to wait and see if things turn out okay, only to lose puppies and/or mom.