If you placed them into the incubator on 18th April then they are "at a minimum" - 14 days into incubation (plus any days previously incubated).
Given your pictures I would not consider them much past that 14 day mark - so, if it were me, I'd work on the assumption that the hen hadn't started...
As an example - I have several sets of eggs in incubation at the moment - I just went now to take pics for you to compare with.
You can see the different in air cells and embryo development.
Your eggs look quite similar to my Day 7 eggs - perhaps a few days further along?
Eggs at Day 7 of...
As an additional note - it may be the location of the torch in the pictures, but I cannot easily see the air cell. If you are confident that your humidity levels have been correct then you can also age the stage of incubation by the air cell size.
I can clearly see the embryo so I'd say past day 7, but the embryo is not taking up much of the egg so I'd say, as a rough guess, those eggs are approximately 8-12 days into incubation.
When did you put them into your incubator??
Hey Hey :)
If you have pictures of your candled eggs I'm happy to give you my estimation on their incubation age. In the meantime - here's a chart that I used to find useful when learning to candle.
If your eggs are starting to draw down then I'd say it's safe to stop turning them. In my...