While eggs develop humidity will move around a bit, as the humidity in the HOME air varies (heat or AC changes that) the incubator humidity moves. So even a lot more sun coming in can change things.
That's why it's best to locate it in the most stable room in the house. In mine it's the furthest room from the HVAC, without a south facing window.
What humidity works in any one home, city, state and country varies hugely. So you just learn to find what works best. I run mine dry. Some people have to fight up the humidity the whole hatch. I only pay attention if I have shipped eggs that might have lost moisture in shipping.
When I used a "normal" humidity my hatches drowned. Really depressing.
I added more eggs yesterday so they're now five days apart. The results should be interesting.
My first possible frizzled del or rock has been hatched. Half the size of a normal chick, black and red, yellow feet. Cute little spud. He's running with his sibling delaware/partridge rocks. He looks like a dwarf.