I agree with locking them in the coop. Most of mine lay in the early part of the day but I have hens laying an hour before dark too.
You may have to keep them in the coop for several days Sam.
They won't like it but once retrained to lay in the boxes you shouldn't have to repeat it.
The only other thing may be number of nests vs number of hens.
With my layers one nest per 4 hens works well. My broody group has 6 birds and 4 boxes.
One bird is no longer laying and one is a non broody breed so we will see how that works over the summer.
You may have to keep them in the coop for several days Sam.
They won't like it but once retrained to lay in the boxes you shouldn't have to repeat it.
The only other thing may be number of nests vs number of hens.
With my layers one nest per 4 hens works well. My broody group has 6 birds and 4 boxes.
One bird is no longer laying and one is a non broody breed so we will see how that works over the summer.