Again my info is old (2018) but IIRC the breakfast was one person manning the register & there was a several person backup, everyone had the all day dining. And I was impatient because it was early & I hate wasting that early time, so that may have colored my perception also.
When I did it again in 2021 / 2022, we activated at early lunch and there were multiple registers open so it wasn't waiting for one person to process everyone. And/or the person doing it was maybe more speedy / I wasn't feeling as rushed? Either way, it didn't seem to be nearly so painful a process as I remembered from the first time. You do have to specify if you want an all day dining bracelet or if you want to present your all day dining receipt each time. Once they process it, they can't change it, and they didn't ask so I had to carry around the paper all day which I wasn't expecting.
I think they have the dining hours for the various restaurants listed online?
Overall I have found the all day dining to be a great deal if you are in the park most of the day (especially if you can get it at a discount such as a black friday deal), it's just the initial activation that was clunky. The food is decent/good and there is plenty of it. The dining plan is pretty user friendly with a variety of options all color coded so you can easily tell what items are on the plan.