Incubating duck eggs with different stages of incubation

[quackkquack__]

Hi again!!
So I have 4 call duck eggs in the incubation, they were all put in at the same time, April 29th.
Even though they were put in at the same time, they started developing at different times. By day 3, I could see a small formation of a heart in eggs 4 and 8. By around day 4 or 5, I could see a small formation of a heart in eggs 6 and 7.
Currently, egg 4 looks quite dark and looks ready to hatch within the next few days. Egg 6 and 7 looks a few days behind (but still quite active with movement) and egg 8 only looks like a couple days behind egg 4 (oh, forgot to mention they are on day 20!)
I'll post pictures sometime tomorrow (since its currently 10:30pm and I have school tomorrow) but I'm a bit unsure of when to stop turning them and when to expect ducklings ^^'

 

[quackkquack__]

I currently can't get photos of the eggs because I'm at school but according to this picture:
Egg 4 and 7 looks like day 24/26, egg 8 looks like day 20 and egg 6 looks like day 16/18.
(I do now realize I was wrong about 7 looking a few days behind ^^')
When do I stop turning these eggs?? (Currently on day 21)

 

[quackkquack__]

Not the best photos since I was rushing and my camera quality was bad for a few of them, idk why

Egg 4:

(Didn't get any good pics of 7 but looks just like 4, super dark inside can't see anything)

Egg 8:

Egg 6: