In the month of

These are the things that John wants to do in / on / at the month of May.

Hi,
These are the things that John wants to do in / on / at the month of May.

More common is
These are the things that John wants to do in the month of May.

Clive

True, Clive, but "in the month of May" has a certain poetic 'je ne sais quoi'.......

Hi,
O the month of May, the merry month of May,
So frolic, so gay, and so green, so green, so green!
O, and then did I unto my true love say,
Sweet Peg, thou shalt be my Summer's Queen.

(Thomas Dekker)

Clive

Could you tell me the difference between this IN THE MONTH OF in question and the following AT THE MONTH:

-She's leaving at the month, and she's crying a good deal at night.

She's leaving at the month, and she's crying a good deal at night.
This is incorrect English.
'At' relates to a specific point in time.

Say eg She's leaving at the end of the month, and she's crying a good deal at night.