It depends on how many times you wish to ride TSMM. It is our favorite ride in DHS, so we always ride it twice via SB line first thing in the morning as the lines will only get longer as the day progresses. We use the FP+ later in the evening, giving us 3 TSMM rides for the day. (before FP+, we rode it 4 times/day).
We ride RnRC via the single rider line, which always moves quickly and can ride 3 or 4 times/day with no problems. It is ToT that is hit or miss. If you are there at the right times, SB can be short. Time it wrong and the wait seems to take forever, and I hate that queue.
To answer the OP's question - we arrive at DHS 45 minutes before the advertised park opening time. They usually start letting folks in about 15 minutes before the advertised time on days without morning EMH.