If you want to cancel/book your PRS ticket of LKO mail (and some other trains) at the last time (after 8.00 pm) here is a tip for you.
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Go to the Current Reservation counter which is situated at the main entry of LKO station and cancel/book your ticket. It opens till 11:00 pm.
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Note:...
more... Be careful if you ask someone for current reservation counter because most of the people there don't know and can send u to the reservation counter which is in a separate building and this will lead your time.