I am planning a trip with a connection through SIN to my final destination of Bali. I will be arriving on separate tickets as well. I am set to arrive at 645am and am hoping to catch a flight at 1015am. Is 3 1/2 hours enough to make that connection? I am assuming I will be changing terminal. Do I actually have to pass through immigration or can I use a transfer desk? I am hoping to check my bags all the way through to Bali (I am flying United DEN-SFO-SIN and Scoot SIN-DPS).