Not really sure, but I don't think that they'll start growing unless they hold around 99 degrees for a couple of days. Our holiday keeper put six eggs on a shelf in the coop that can reach 120 in the sun, and at least five of them were starters.
The eggs in my incubator 'gun out' around 94, the...
I'm going to guess that once she gets her 'brood' together, she'll do a three day dedication to get them started.
Have you considered picking up an inexpensive hand-held non contact thermometer?