how long should i hold out on live?
It depends, snakes metabolism is very efficient and they can go weeks or months without food, however the real question is can you do that with the animal in question.

If your animal is old enough and has a good body weight tough love might be required and it could last weeks or months.

Important things is do not try everyday, if it fails try again the following week or even 2 weeks later, offering to soon after a refusal only lead to more refusal.

Trying thawing at room temps right next to your snake enclosure and than warm up the prey with the hair dryer (if you not doing that already)

You are offering the same type of prey correct?

Switching can be tricky patience is always the key.