[edited - I agree with Phil.]
The general answer is "at" a time, "on" a day/date, and "in" a period of time such as a month, season, or year. "To schedule for" a time, a day/date, a period of time is correct. I use a mix of "schedule for" and "schedule at/on/in."
The Collins dictionary is a good resource.
verb [usually passive]
If something is scheduled to happen at a particular time, arrangements are made for it to happen at that time.
A presidential election was scheduled for last December. [be VERB-ed + for]