We were at DCA yesterday too. We decided not to push it an early arrival after getting in later Friday evening and knew we would be back aways on RSR FPs - and we were. We arrived at security at 7:40 from Harbor side and were in the RSR FP line by 7:45. At that time the line stretched back to past Disney Jr Playhouse but not quite to the Off the Page shop in the Disney Animation building. Soon after that the line wrapped all the way back past the Disney Animation building. I could not see how far.
We got our RSR FPs at 8:19. So in all we waited about 35 minutes in the FP line. Our return window was 11:15AM-12:15PM. There have been rumors that Disney does not give out the full complement of FPs for RSR as they do for other rides. So there are even less available. Like one-half to one-third. It might have been because the ride has broken so much and they did not want the FP holders swamping it during times it is open.
To other questions asked in this thread, I do not know how long the FPs lasted but it was at least until 9AM but I think they were well gone by 10AM.
As has been well documented in other places, the RSR FP machines are not near the ride but in front of the Its Tough To Be A Bug ride.
We rode RSR around 12:30 and the wait in the FP line was pretty short. Maybe 10-15 minutes. That was compared to a consistent 90-120 minutes all day in the regular standby. I rode the SR line Friday evening at 7PM and it took a full hour.
So is it better to wait and get RSR FP in the morning like we did for 35 minutes, and then wait in the FP return line for the ride for 10-15 minutes like we did, in order to avoid the standby line? Hard to say. If we had chosen to arrive earlier at the DCA gates then maybe. Overall I think we made a good choice for us but it is not an obvious choice for others.
After we got our RSR FPs we rode Luigi's Flying Tires and then went to TSMM around 8:40 and the line was posted at 15 minutes but was actually a little over 20. So altogether we had a good morning. It is just hard to say whether getting those FPs was worth the wait. It sounds like the OP waited almost an hour for them (arrived by 7AM). Was that one hour wait for FPs worth it?
One solid advantage of FPs vs. Standby is that you can use them anytime. Which means if the ride breaks down you can come back at any time and use FP. If you are in standby and the ride breaks you have a huge dilemma if you have already committed significant time to the ride. Should you stay in line and hope they get it going again soon? Or sacrifice the hour you may have already spent and come back later and wait in line again? That is probably the best reason to gut it out and get FPs in the morning IMO.
Other RSR things of note. When I rode RSR SR line for the first time Friday evening thru SR at 7PM, the SR line was all the way out past the entrance a good bit. The CMs told everyone the SR line was a 90 minute wait from there. I was waiting for DS16 to arrive from LAX and so chose to just wait it out. And it took 60 minutes rather than 90.
Last night I got to the SR line at 10:58PM and the park closed at 11PM. I was second to last in the SR line and the lady behind me bailed after awhile so I was dead last in SR. It took about 35 minutes for me to get on the ride. The final folks in the standby line were about the same - maybe five minutes more. I could see the end of the standby line as I got to the boarding area. And when I finished the ride there was no one else in line boarding. That means standby at 10:59PM at night on a Saturday night was about 40 minutes long. For anyone thinking of using this strategy!