Which means you land at 0915 in Mumbai, but considering that you need to collect baggage from the carousel etc. that maybe 945-10AM, and even then its ok, you can make the international airport within about 30 mins. You will have some traffic jam for sure. I think you should step out, and board a taxi/auto real fast, that will be the fastest but you have to pray that all things fall into place a little as it is a little tight. I will also advice you you to do a web check-in for your international leg so that you have that extra bit of time.. Good Luck!

Rgds,
Vikram