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Your hens won't pay any attention to the eggs unless they go broody. Normally, that's in the spring or early summer, though there are exceptions. Some breeds don't go broody at all, or at any rate, very seldom.
Until a hen is broody, she's not actually a "mother hen". She's just a hen who lays eggs.
Until an egg is incubated, there is no baby chick, even if the egg is fertile. It's just an egg.
Normal incubation temperature is 99.5F-100.5F. Normal human body temperature is 98.6. It's not much, but that single degree can make quite a difference in the health of the chicks, and how long it takes the eggs to hatch.
Most of the time when eggs get hatched in somebody's bra, it's eggs that have been set on by a hen until near hatch, then for some reason, (hen leaves the nest, or gets killed, or eggs were added after the first day, so there were multiple due dates and the hen had to leave some to care for the chicks that already hatched, etc.) there were eggs with no hen, and people decided to try to finish incubating them. I did that once myself, many, many, years ago. The egg hatched, too.
There was a BYC member who hatched some eggs this way, and did the whole incubation in her bra. So it can be done, but I'm not sure you're in a good position to pull it off, what with school gym class, and so on.
If you don't have a developing embryo by 5-7 days, you might want to wait until you can buy or build an incubator, and try again. Your hens will still be laying fertile eggs. You could save eggs and set them aside, at room temperature, until you have the number you want to incubate, then start them all at once.
Whether your eggs hatch or not, this will be a good learning experience for you. Good luck to you, please keep us all posted on what happens!