Prepositions of time

[Melody]

English Grammar Tests, Elementary Level

ESL/EFL Test #91 "Using Prepositions", question 6

Due to his new shift, he has to wake up ......... 3 a.m. every day.

(a) in
(b) at
(c) on
(d) from

English Grammar Tests, Elementary Level

ESL/EFL Test #91 "Using Prepositions", answer 6

Due to his new shift, he has to wake up at 3 a.m. every day.

Correct answer: (b) at
_________________________

I want to get an explanation.

Melody

[Mister Micawber]

.
The general usage is:

at a time -- At 3 pm
on a day -- on Tuesday
in a month, year, etc --- in June, in 1997.
.
_________________
Canadian-American native speaker
who teaches English for a living at Mister Micawber's
ESL cafe: Interview with Mister Micawber