How long does he have to wait before he can eat again after a crowning?

A few hours. If it's the first step of getting a crown, then don't eat any food until all of the numbness is gone. In addition, some temporary cements take a few hours to set completely. If it;s the second step where the permanent crown is fitted, sometimes you are numb, sometimes not. Again, don't chew if there is any numbness. Otherwise the final cement hardens very quickly.
Soon. Once your anesthesia has dissipated you may eat what you like. If you have a temporary crown then use common sense with your diet until final crown has been completed.
Same day. A crown can usually be used for eating right away, although i reccommend to wait 2-3 days to allow the tooth to heal from the cementation.
Eating after a Crown. I advise all of my patients to wait until the effects of the anesthesia have worn off before eating. Typically, this takes about an hour after the dental appointment.
Immediately. Modern permanent cements used for placement of crowns set up within 10 to 20 minutes. Some resin cements set up immediately. You can safely eat on a permanent crown as soon as you leave the dental office.