Prepositions of time can be used in the following ways:

in: with longer periods: He started studying in October last year.

at: with times of the day: She has a doctor's appointment at 4 pm.

on: with dates and days: Mark is arriving on Saturday.

during: for a period in which something happens: During his exam, he was called in to the principal's office.

for: to tell how long something lasts: She was out of the office for 5 days.

since: to describe a point in time up to now: I havent't spoken to him since Friday.

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