I did a turnaround at DAC on TG 2 years ago (see
trip report). I'm not sure exactly how long a transit time I had, probably 90 minutes give or take.
That was long enough, even with a quick lounge visit. However, the transit facilities are almost non-existant. Since I was unable to get a return BP (I don't know if SQ has the same issue or if it has changed in the past 2 years), and there is no airside check in facility someone had to go landside to check me in. I didn't need a visa.
In my experience TG has a higher tolerance than SQ for odd itineraries (incl turnarounds). It is possible SQ may deny boarding if you have no visa.