Why I am not able to cancel order after 3:30?

Why do I have to wait till 3:40?

Hello Trader,

At 3:20PM the RMS computer ( RISK MANAGEMENT SYSTEM) take over the control of your trading positions and orders.

ALL your pending MIS orders get canceled at 3:20PM

ALL CNC orders pending after 3:30PM will be carried to the Post Closing session of the exchanges from 3:40PM to 4PM.

Such CNC orders on your account can be modified and canceled only between 3:40 and 4PM

There is no point in carrying that order to post closing session as it won;t get executed.
Sometimes I don;t have enough margin because this order is still there, Then, I need to first cancel it and then place the order. Even this delay can sometime cost me…