Seperate tickets or one ticket (PNR) ?
Will you have checked or hand luggage only ?
90 minutes MCT is acheivable but checking in for the dom flight at the T1 int terminal and connecting on that bus can take a long time. Often better to take the train (any pay) for T1 to T3 transfer
I have have trips with one PNR-ticket with 55 minutes T3 to T1 but checked baggerd has not made the T1 flight.