I don't wait any certain amount of time for my animals before assessing and fixing what can be fix, but than again my animals rarely fast as well.
First thing is that I feed smaller preys once weekly and skip a meal every now and than.
Second I make sure their husbandry is optimum, not drop in temps especially in the winter) etc. During breeding season I house males in enclosure smaller than the usual to ensure they will keep feeding during the season. Bedding might be switch as well.
Third patience everything is optimum, the animal is healthy and we'll hydrated that is all you can do.
The only trick I use for animals that fast without any particular reason even after everything has been tried is a car trip, I put the snake in a snake bad and go for an hour ride, and it works.
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