After how much time should I get really worried if my baby corn snake isn't eating?

Hello!

I've bought my very first baby corn snake last Sunday (on the 17th of October). The breeder told me that he (the snake) last ate on the 12th. He allegedly already ate frozen/thawed pinkies succesfully.
After bringing him home I've let him adjust to his new surroundings (small plastic box with coconut fiber as bedding, a small water dish, plenty of clutter and two hides). He seemed pretty chill in the past few days, mostly hiding, only coming out exploring sometimes in the night.

My problem is that when I try feeding him a f/t pinkie he seems more terrified and trying to escape than hungry. He is not my first snake so I'm not 100% unexperienced feeding them but him rejecting food still makes me feel very anxious and panicky about his health and well-being since he is so tiny. I'm sure he shouldn't go without eating for so long.

There are plenty of good feeding tips on this forum and I'll try them all, but my most important question is that after how much time should I get really worried if he doesn't eat?

I would start worrying after a month or two. You only got him a few days ago. You need to leave him alone for at least a week before you offer food. When you're ready to feed him, I would wait until evening, then place him in a small container. Leave that container in a dark, quiet place for like 30 minutes. Heat up a pinkie super hot. You can even dip it in boiling water for a few seconds. Drop it in with him, close the lid, and leave him totally alone in the dark with it for an hour. Check on him at that point and if he hasn't eaten yet, reheat it and leave it with him overnight. Baby corn snakes are prey for a lot of things in the wild. Your best bet for getting them eating is making them feel totally safe and secure. If you're hovering around or trying to tong feed, it's just going to stress them out.