That's a bit optimistic. I think it should be OK as long as there are no delays, but considering it will take probably 10-15 to exit the aircraft and get to the curb at T7, another 10-15 minutes to walk to TBIT, and another 10-40minutes to clear security, it's hardly 'plenty enough time'. More like 'just barely enough time'

If the flight boards 45 before departure, one could easily not get to the SQ gate until boarding starts.

This is a tough decision. I think I'd leave it as-is but I would consider standing by for the earlier flight if I had the time or felt like the extra peace of mind.