Off Season Throwing.

Should a High School pitcher take any time off from throwing?
In the off season, (November, December, & January)
I figured at least once a week of 10 minute long toss, before preparing for the next season.

Unless you have a sore arm of some other problem, THROW EVERY DAY.
My pitching coach—and a lot of others—used to advocate this, and even if it’s just fifteen or twenty minutes of playing catch, it’s an excellent idea. It keeps the arm from getting stiff, and you can even use that time to work on a new pitch or refine an existing one. If the weather is too cold to do it outside, there’s always some place like the school gym or (as in New York City) an armory where one can go inside and do some throwing. I used to do that all the time, and it kept my arm loose and flexible, as well as giving me an opportunity to work on my slider. You can always find a catcher. 8)

I agree with Zita.