I actually goofed - today is actually day 19 (long weekend here this past weekend so I am all mixed up with the days!) duh! I am counting from the 24th Sept (even though I put them under her on the 23rd).Yes it is a good sign you can only see air space with the rest of the egg appearing dark at day 17. Try to find a brighter light for next time if possible, but it sounds like they are good to go! You dont want to move or rotate a broody's eggs during the last 3 days. The chick is nearly fully developed will soon rotate into hatching position. The broody hen puts her eggs in "lockdown" same as with an artificial incubator.
I continue to encourage my broodys to exit their nest boxes to for eat, drink and poop even while chicks are hatching, after occurrences of broodys pooping in nestboxes on eggs and hatched chicks. Especially if you expect eggs to hatch early, 2-3 days may be too long for your broody to hold her poop. I see you are in Canada, but she wont need to stay out long, no more than a few minutes. Unless your temps are already very cold, any hatched chicks wont get cold in a few minutes time as long as they are dry.
Here is a photo of hatched chicks and even eggs that are pipping! Photo was taken last october 2020 while mom was out for a quick break.