Fill in the blanks with appropriate preposition :-

The train leaves _________ 5.30 a.m. from platform number 8.

at

The correct preposition to fill in the blank is at.

The complete sentence is:

The train leaves at 5.30 a.m. from platform number 8.

The preposition "at" indicates a specific time or point in time. It is used to convey the exact time of departure of the train.