Both of these sentences are okay, but "You should make a schedule for watching TV" is a bit more natural. The reason the second sentence works is this: In English, we do not use the infinitive after a preposition. so, "for to watch" or "for watch" are incorrect. When we use a verb after a preposition, we use its -ing ending. This is one use of what is called a "gerund" (a verb that functions as a noun. I hope this helps.

A time table is alright. I would say you should set a time limit for watching t.v. Meaning the t.v would then be someone else's turn after the allotted amount of time is up, or that it would be shut off at the end of the time limit.