I think two or three meals is probably typical. Let common sense be your guide. When you feel the snakes are well started enough so that the typical hobbyist can get them going and have them thrive, it's probably time to start offering them.
The risk of selling them too early is that if the buyer is inexperienced with that species, or snakes in general, they may not be able to get them feeding, or other husbandry problems may occur. While this may not be your fault as a breeder, you probably don't want dissatisfied buyers, and you probably don't want the babies to suffer and die.
The best time to sell neonates is generally when they are reliably feeding and well past the "delicate" stage. You may also want to factor in the experience level of your buyers.
