It can be delayed because of several reasons. Could be technical problems and they're waiting on some parts to fix the plane. Could be issues somewhere else and they've had to divert aircraft etc. etc. The best way to check where the delay has happened is to use a site like flightaware etc. to check the status of the incoming aircraft. That will tell where the issue has risen but not what's caused it.

Most likely explanation - since BOM is shutting its main runway everyday for maintenance all through the day till about mid Feb and causing major delays for all aircraft using the airport, Jet would have decided to reschedule some of their flights to ease congestion at the airport and use the airport only when the main runway is open.