in：后面紧跟大的时间或者地点（早午晚，年月季）

in the morning / in the afternoon / in the evening

in Jan / in 2020 / in spring

at：后面跟小的时间和地点

at noon / at night / at half past six

on：后面跟具体的时间

on May 1st / on Monday / on Children’s Day / on Monday morning