Read, translate and remember. Compare English and Russian prepositions used in these time expressions.
On is used with a day; day + morning / evening / afternoon / night; a date; a special day:
on Sunday
on Friday morning
on 5th July
on Christmas Day
In is used with a month; a season; a year; time of a day; a period:
in April / March
in winter / spring / summer / autumn
in 2017 / 1825
in the morning / the evening / the afternoon
in 5 minutes / a week / a month / a year
At is used with time; mealtimes; festival:
at 7 o’clock
at lunchtime
at Christmas
And also: at the weekend, at night