Due date for form 23b for fy 10-11 and 11-12 ??

Hello everyone,

i have to do audit of a pvt ltd co having authorised capital of rs.100000/- for the fy 10-11 and 11-12.

i want to know the due for filing form 23B (DATE OF EVENT) for appointment of auditor for fy 10-11 and fy 11-12 so that i can calculate the late filing fees and make appropriate provision  in the books of accounts.