Hi Bernardsmith,
Usually draining is simply getting rid of "most" of the loose whey. The pressing will take care of the leftover loose whey. Traditionally, one would not want the curds to get cold before pressing, so that tells me not more than a few minutes, if it does require more time to drain, I put the strainer over the still warm pot and cover it... Or pull the corners up of your cheese cloth/butter muslin and hang it in the pot using a dowel or cooking spoon. Most of your draining knowledge will come from experience and reading cheese making tutorials. Each cheese type will have its unique needs. Our job as cheese makers is simply to give the specific cheese all it needs until it's ready to eat.