It can take a few days. I remember when I got one 10 years ago, it would hide. I would drop food in the tank and then back away and stay still so it would venture out and eat. After a week or so, it stopped being shy. That tomato clown was with me for a little over 10 years. He was caught in the wild. I don't think there were captive bred clowns back then at least for sale.
I recently got a pair of tank raised tomato clowns. As soon as put them in the water they turned around waiting for me to feed them. I never expected that type of behavior.
After they do settle, be prepared for some aggression. The hostilities started a couple weeks after going in my tank. The dominant one was pretty mean. The unlucky one developed a fungus after being chewed up a bit. The LFS said nothing could really be done, try feeding some NLS fish food. In about three weeks, the fungus is mostly gone. I don't believe the food cured the fish, just provided good nutrition to keep up strength and recover. The fish go nuts over that food.
Ivan
