score:3
Having done this, I can confirm I needed no more than about an hour to get through security and exit immigration - although I was travelling through the "business" lane for both (not in Business, but I have OneWorld Sapphire). Mumbai seemed very efficient. If I were doing the journey again, I would arrive 2 hours before, just in case.
Upvote:3
With the speed of India, it could be longer than 2-3 hours. Also, I'm not sure if this is still true, but BOM airport always seems to be under construction, so the shortest route through the airport could be closed. Since you're Sapphire, the business class check-in lanes aren't that long usually. I would strongly recommend checking in online to reduce check-in time, even if you have bags. I don't think BOM has a bag drop area, so you will need an agent to tag your bags. I read (I went to India 8 years ago so I don't remember) that everyone gets a pat-down, so the lines will be considerably long at security. I think there are also priority lanes in security, so you may experience a shorter wait time. I would recommend 4 hours just to be safe.