I put together a whole notebook this year of what sells and when, so I'm qualified to answer this one
I started hatching in January last year. Day olds didn't sell in the winter, but those started pullets got gone as soon as I could sex them. Day olds started selling in March, and my phone was blowing up from 2 weeks before Easter to a week after for day olds of any breed. Demand was so high that I was selling day old straight run for $10 each, and had people waiting for me to hatch again. I planned my Easter hatch to hatch the weekend before. That gave me time to get them advertised, and a few days to make sure that all of the chicks were healthy. Feed store chicks were no competition. If you have pure breeds and a nice setup, there are plenty of people, at least here, that know my chicks are better than the feed store's.
2 weeks after Easter, sales died. I couldn't sell day olds until the weather started cooling off again. You could pretty much schedule your sales to the daytime high temperatures. If it was over 90 degrees, no one was buying chicks. Pullets always sell, and I end up giving away a lot of roosters, but if I hatch in the summer I have to have dedicated grow out pens. As soon as the temperatures started dropping and people started thinking about the fall, I started getting the calls for chicks again. Now that the weather is about to turn cold, no more chick sales, but I have people begging me to sell my BCM pullets.
So, moral of the story is: Hatch in March for Easter chicks, hatch early fall for winter chicks, pullets are always in demand, and have a plan to sell, eat, or give away cockerels