Personally myself I do not like to candle to much. Darker eggs are a tough cookie at times to see thru.We got our eggs from Merton Feed Company. They are all Black Sex Link and are all darker brown eggs so they are tricky to candle. I tried candling at the 7 day mark but there were too many that were iffy so its suggested I hold off and candle later. I'll just try to make sure none of them are rotting or weeping.
I like going thru the eggs and candle once, than mark the iffys and spot check.
Not going to hatch this year. Just buy a few,
Might thin down the flock for next fall and just keep a few for eggs for ourselves. Really not much money in selling eggs.