I don't recommend arriving at DCA's opening.
1) DL is always more crowded than DCA. So, use the less crowded morning hours on DL instead of DCA. You don't want to be standing in line waiting for DCA to open at 9:30 when DL crowds are relatively low.
2) For the same reason, DCA is much more easily toured in the afternoon. The only rides that generate really long lines are Soarin, California Screamin, Sun Wheel, and Grizzly River Run (on hot days). All of those have Single Rider and Fastpass except for the Sun Wheel. Also FP is available for Mulholland Madness and Tower of Terror, so if those happen to have a semi-long line, you can use FP there. You shouldn't be worried about long lines at DCA except during extremely busy seasons.
However, the one exception I will make is if you are going to be touring this summer (or late this spring). The new Toy Story Mania ride will be opening and it will probably not have FP. It will generate long lines, especially during the early summer months and continuing through early September.