In my thus-far-educated opinion, you should ALWAYS offer your snakes food on their regular schedule, whether they're fasting, shedding, or just being difficult. The only time you should Not offer food is when the vet says no because the snake is injured or ill.

In time, everyone learns each snake's preferences. Some will eat no matter what all year round. Others will only refuse when in shed. It's best to just try try try and see what happens.