Guys, we use in for nonspecific times during a day, a month, a season or a year.
Example :
Teachers always start their work in the morning.
In the dry season, farmers often use water pumps to water their fields.
And then, we us on to designate days and dates.
Example :
Do you usually have a hoisting flag ceremony on Mondays ?
Weekend is on Sunday.



Next, we use at to designate specific times.
The rain stopped at 9 a.m.
We arrived at Diponegoro’s street at 10:30 a.m.