When should I hatch chicks?

When's the best time to hatch chicks to take advantage of spring pasture?  I'm very happy with our March 2 hatch, which allowed me to let the chicks out into the outside world on March 16.  The greenery is tender enough that they can eat gobs of it, so I haven't had to hunt down succulent growth especially for them.

Granted, this has been an obscenely warm spring so far, and it might have been too cold for chicks to be out and about in a different year.  I've got a second set of chicks slated to pop out of their eggs at the beginning April, which might be a more realistic time for chicks if you live north of our zone 6.

Another factor to consider is trying to get the chicks fattened up by the beginning of the summer pasture slump.  If you're buying Cornish Cross, that won't be a problem since they're ready to eat in 6 to 8 weeks, but we grow our heirloom broilers out to 12 weeks.  Will the pasture still be lushly growing a the end of June?  We'll have to wait and see if better management this spring will ensure good chicken forage that late into the summer.