Chhatrapati Shivaji International Airport has a Baggage Storage Facility known as the Left luggage, which accepts bags for safe keeping up to 90 days.
As per the airport website, the minimum charge for safe keeping a standard size bag is 200 INR per bag and it is 270 INR for a larger bag for up to 6 hours. The charge increases with time.
From the official website, the storage facility is located at International Terminal 2, (Level – P-4, Zone-6). Left Luggage is better known as “Cloakroom”.
I could not find any info on queue at Left luggage but the Queue timings of Bombay airport are generally high than other airports as you can see in the customer reviews. So expect and be prepared for a long queue.
You can fine more information including contact info at the airport website.