It can take more or less time before it kicks in.

I had to assist 2 hatchings in the past one for 3 feedings the other for 6 months before finally one day she decided to eat on her own.

Make sure your BP his in a tight enclosure, switch to aspen bedding if haven't done so already, provide proper temps etc and keep trying.

It always hard to say when to give up but obviously at one point or another the animal will have to eat on it's own.