1. The exhibition opens at 10 a.m. on Sundays.

2. Dad will arive late at night, so I will see him only in the morning.

3. We don't go shopping at weekends.

4. Jane was born on the 15th of December in 1989.

5. The snow usually starts melting in spring, in April.

6. Mike has lunch at noon.

7. I will call you back in 5 minutes.

8. The students will write a test at the end of the week.

' at ' - точное время

' on ' - общее время ( дни/даты )

' in ' - какие то большие периоды ( месяцы/годы и т.д. )

  но:

' on ' - с днем рождения  ( on birthday )

' in the future '

' on the present '