If I recall correctly, I've read somewhere, NSE revises margin 6 times a day !!! Once at open (or is it before open), 4 times during market hrs & finally after close. Maybe that's why margin blocked changes everyday. This also means if there is large volatilty the margin can be revised drastically & you can be asked to pay fresh margin in addition to what is already blocked, this in turn means you should not invest total funds but keep margin revision requirement funds handy to avoid auto sq off.
I think, (often I am wrong
) your position will get best return when you let exchange automatically exercise/settle the positions on expiry, but STT (at several times more than normal rate) is charged for exercising the short options. This is for ITM. So if you short you pay STT (normal rate) & if this short is exercised/settled on expiry by exchange you again pay STT (at several times more than normal rate) !!!
Maybe, if option is liquid & ITM you can cover position a few days before expiry to avoid STT (at several times more than normal rate) as buying option is not subject to STT.
Play safe keeping Nick Leeson in mind for what not to do with options.
confusion..confusion
Expert's comment invited...