Mysterys of hatching

Today is the 27th May, our chicks are due to hatch tomorrow, the incubator is constant at 37.5 .
The first chicks, two Jersey Giants arrived on the evening of the 26th, just 18 days incubation.
At 8am this morning five more had hatched, 2 La Bresse, 2 Light Sussex and one more J.G. a further La Bresse has hatched with with a further seven pipped.
To me this is a mystery.
Chicks are incubated for 21 days, not counting the day you set the eggs. So why should some eggs hatch earlier than others? Admittedly I can't be too sure of the age of the La Bresse eggs, they were a gift in exchange for a dish washer that we inherited when we moved here,( I don't like the things and would never have used it,) but the other set eggs were from our own birds and would have been no older than two days. It rather looks as though the hatch will take place over three days.

No matter how many times I watch eggs hatch, it is still, to me , a miracle.

All the other birds that we have hatched are doing well, the birds destined for Sunday lunch have their diet supplemented by sprouted grains, including Organic soya beans, the birds love this and are putting on weight well, we expect to be eating the first one in a couple of weeks time, along with veg straight from the garden.

The potatoes have recovered well from being frosted, not once but twice and have had their first earthing up, the celery has had a bashing from the slugs, I never thought that slugs would attack it, we have made collars for them now out of cat tins, we try not to buy any plastic bottles although they do have their uses, and Simon refuses to let me go scavenging for them in rubbish bins, so the cat tins have to suffice. The spinach was doing very well but before we had time to harvest any the young rabbits had a break out and enjoyed some of it, then came the sun, the past week has been hotter than Spain and we have been without rain for some time, the effect on the spinach is not good and it has started to bolt. Everything else is fine, so far! although we are getting rather fed up with strawberries and mange tout peas.