I thought I'd share some of the FB thread below. I did the DL half in 2014 and left the Anabella at 4:30. Zero issues and plenty of time. This year I am staying at DLH and planned to leave at 4:45. Based on the FB thread, I've changed my mind.
Multiquoted a bunch of folks so you'd get the alert

See info below the quotes.
Thought I would tag everyone inquiring. From the same FB thread here is what has been shared.
The reasoning for this is that race and spectator locations will be closed at 2:30 am and reopened at 3:30 am for security check. Just like the one you go through at the esplanade before going into the parks and will include a bag check (not sure if this includes race belts). The lines will be mandatory and will be setup supposedly before the corrals, near the finish line, and before entering the family reunion area. This is the first time they are doing this so it will probably get hectic because people are not used to this, nor is race staff and the parks totally sure how this is going to work. So like usual there will probably be people getting upset because of the lines and time this takes so please arrive early if you want to make sure you are in your corral on time. And be patient. These are new checkpoints, never been done at Disneyland for races. I don't know if they are going to ask to see contents of race belts or not. But if you are checking a bag at Bag Check you will go through a checkpoint before you can drop it off. I was just told to emphasize to people to get there early because it will make things not as crazy at race time and to tell spectators to pack light if they are going to watch at the finish line or meet you in the reunion area. The concern is if they do require everyone to be in lines to go through a security check before entering the corrals (which is what it sounded like may happen) is that it will get a little crazy at 5 am when 15,000 people are trying to get into their corral.
So basically there is bag security check and then gear check. Which could slow things down a lot. This is a security thing, I don't see how it will help the corral issues other than making it take longer to get to your corral and riskier if you are on the later arrival side.
W&D apparently had this extra bag check BEFORE bag check and it was a bit of a mess. I thought they did this at PHM as well but I may be mixing it up with another race somewhere else. I don't remember it slowing things down too much at PHM.
In theory, there will be a separate line for folks without bags. But because there just isn't a lot of space there to do this, like there is in FL...even if you aren't doing gear check it could be slow. Especially if they are checking race belts too.
I haven't yet decided how early I am going to leave. To be honest, I'm going to wait for reports from the 10k as I am not doing the challenge, to see how that process went. But UGH. One of the advantages of the CA race was a bit more sleep and that seems to be lost.