Unlike us, reptile eggs are somewhat dependant on the temperature...so if they are kept at a lower temperature they take longer to hatch than if the temperature is higher....but don't just think that increasing the temperature is the thing to do. Nobody knows the exact temperature that will produce the "perfect" babies...if they are incubated at temperatures that are too warm or cool they could die or be smaller and less healthy than if done at that "perfect" temperature.
In addition to this some eggs go into diapause and that can affect the length of time that the eggs will need to be incubated for too....so...there is no definite time with chameleon eggs.
Patience is a virtue that you need to have with chameleons!
For eggs from veileds for example...the eggs will grow a good deal. They will look good and white as a rule. As they near the hatching date (like maybe a week or two before) they could get what I call "windows" in them....marks on the shell that don't look as white or solid as the rest of the egg. They should lose water so you may see "sweat" on the eggs a few days before they are going to hatch....and as they lose the water they will shrink in size and may even dent in a little. Next you should see a slit in one end of the egg and likely the baby's head will be sticking out. The baby could lay like this (eyes closed) for several hours or even a couple of days. Its absorbing the yolk and resting for what, in the wild, would be the digging out of the hole. The baby should get out of its shell by itself. Most that don't likely wouldn't be strong enough to survive anyway.
Sometimes the eggs don't get windows, sometimes the eggs don't shrink in, sometimes you will just find that the egg is slit and the head is out. "Nothing" about hatching chameleon eggs is exact. Even how far apart the eggs are in the incubator can have an affect on the hatching. If they are all touching, there will likely be a mass hatching, but if they are spread apart they will hatch more individually and the last one can hatch even a month later than the first. And...if one baby walks over another egg in the container...that can make the egg that was walked over hatch quicker than it would have if the baby hadn't walked over it.
Caution...if the baby comes out of the egg and still has its "umbilical cord" attached, make sure that it can't adhere to something.
Sorry this is so long....but I thought you might be interested.
Just be patient...or pace the floor...or something!