I did Man (UK) to SIN - MDC. With Singapore/Scoot
My initial booking had the same 1hr 30 transit time, they assured me it would be fine.
In the end we decided to extend the trip and did a 24hr layover in Singapore (we checked our main bags all the way through to MDC).
My hand luggage contained all essentials: dive computer, regs, mask, swim shorts, clean clothes for Singapore. I could dive whatever hapened to my main luggage.
Landed on time, got the MRT into Singapore, stayed in Little India, had a great time exploring, then got a taxi back to the airport in the Morning in good time for the SIN-MDC Flight.
Scoot was chaos compared to Singapore Airlines. Everyone was taking loads of luggage into the cabin and there wasn't enough room for it all. They kept trying to put my hand luggage in the hold, i insisted i wasn't being seperated from it.
I would go this route with Singapore Airlines again, they were amazing.