Ответ:
1 IN
February, two days, ten minutes, 2018, the summer, the morning, six months, the nineties, in a moment (BUT AT THE MOMENT)
2 ON
New Year's Day, Tuesday morning, my birthday, July 20th, Saturday
3 AT
at the end of the month, lunchtime, midnight, weekend, night, Easter, Christmas, 10 o'clock
NO PREP
last week, today, yesterday, tomorrow, this afternoon, next week