3 consecutive, unassisted meals, and they're ready to go. If they're fussy, or I had to assist start them, I add a few more on to that number, just to make sure they will thrive.
I've hatched out some 53 gram babies, and some 92 gram babies, already this year, so weight is definitely no indicator! My well-established little guys aren't even up to the weight of my 92 gram newborns yet.
Since 500 grams is the average weight of a one year old on a heavy feeding schedule, you'd have to keep a baby around 6 months, reasonably, for it to get up to 250 grams. Or a year, if it's on a lighter feeding schedule. I don't see that as necessary--if a baby is eating well and regularly, and pooping and behaving normally, that's enough to reasonably show that it's healthy.