My guess (and note that it's only a guess) is that the park probably won't experience capacity closures until late afternoon at the earliest. The lower two levels of APs are blocked and folks do have to go to work and school. The new shows won't debut until nighttime, so my
guess is that if capacity is reached, it won't be early in the day or for a really long period. At Christmas time, when capacity is frequently reached, it happens earlier in the day because everyone (well, a lot of people) are off from work/school the whole day. So, I
think if you got back to DL before 3:00 pm or so, you should be okay. If you waited until just before your ADR, around 6:00 pm, then I think you have a bigger chance of running into capacity issues.
One other option is to monitoring social media and see if anyone is reporting that they've suspended ticket sales. That's usually the first thing they do when the park is approaching capacity. If you hear that is happening, then head back to the park as soon as possible. I don't know if
Disneyland itself would post that they've suspended ticket sales, but I'm pretty sure it would show up on some social media platform by folks waiting in line to buy tickets.