Section 18(3) in The Delhi Metro Airport Express Line, General Rules, 2010
(3)Any route which has been cleared for a train shall not be cancelled until it is cleared by the train entering the route except,-(a)in case of emergency; and(b)in case where operating conditions require that an alternate route be cleared and in this case, the alternative route shall not be made available for clearance until the pre-set time, defined under special instructions, has elapsed from the time the original route was blocked.
