I found dinner very stressful, for reasons PPs mentioned: it is crowded even getting to the check in point, making it harder to judge how to get there no more than 15 minutes ahead (and the CMs didn't seem happy about seeing me at exactly that window, either), and then we gave a phone # to wait for a text to go forward, and then waited on the bridge.
Regarding your desire for an earlier dinner, though. What I have done with other ADRs is, go into the system every few days (or whenever I feel like it) and try to change the reservation. I use my current reservation time and see what comes up close to it. Even if it's just a 10 minute difference, I take it. Then, another few days go by, the mood strikes, and I repeat. I edge my way closer to a time that I really want, and often end up with it on the dot!