I know some1 who's waitlisted, and this is the message they get:
If there is any vacancy exists, waiting list candidate will be issued our formal admission offer letter serially after May 16, 2005. In this case also, you will have to send us your formal written acceptance on the prescribed
form enclosing a Demand Draft of Rs.15,000/- (non-refundable) in favour of IIM Lucknow payable at Lucknow, so as to reach us on or before June 6, 2005.
So the last date for 2nd list payments should be around 15th May...(Note that there's a link for a form as well)