Because I have been on TSMM in the morning when DCA first opened, in the middle of the afternoon and at night, I can say that we had the most success with the least amount of line hassle/stress when we did the early morning route. I think this method was beneficial because many folks are still playing over in DL and will have been there for anywhere from 1 to 3 hours (depending on if it is a MM over in DL and when DCA opens) by the time DCA opens, therefore, not wanting to break their stride in DL to wander across the esplanade to DCA.
I always have to clarify that the way to do the early morning plan is not to arrive at DCA at 9:30 and just stand around until 10:00 a.m. That is the extreme scenario but it's not necessary, and you would be wasting too much time in one spot. I say just leave DL and start heading over to DCA around 9:40 a.m. or so, and by the time you get in the DCA gates and over to where the line is that will form to walk you back to TSMM, you won't be standing in that line for very long, if at all. In other words, most of your time will be spent walking from one point to another point, not just standing in place. The line that forms over by GRR will sometimes start moving (with the helpful guidance of a CM) as early as 9:45 a.m. or 9:50 a.m., putting you in the TSMM queue before 10:00 and sometimes even on the ride before 10:00 a.m. (Again, this is all working with the notion that DCA opens at 10:00 a.m. If it changes to 9:00 a.m., then it's a different ballgame!) In other cases, the GRR line may start heading back to the TSMM area five minutes later and you may get in the queue right at 10:00 a.m., which is still better than getting into after 10:00.
In any case, the line for TSMM builds so quickly that if you stop to do anything else first and then walk back there after DCA officially opens, you run the risk of having tons of people in front of you. When we did the early morning plan and lined up at GRR, then headed back to where TSMM is, we were shocked at the number of people who had lined up after us by the time we got off the ride.
HydroGuy is right that there are two camps. More people tend to agree with his thoughts on the subject, though. That's the more popular opinion. Now that I have read enough other posts from people who have had the same experience I had with the early morning plan, I feel confident that it is effective enough to recommend for those who want to try it. Of course, nothing is fool proof, and you may get a CM who is having a bad morning, and he/she may refuse to let the line budge one second before 10:00 a.m., in which case you may not 'beat' too many people to TSMM, but, again, I have seen enough other accounts of it working well that I think it is worth a shot.