I take Flix a lot and I've never seen them run late, if anything they're early.
Almost always on time. They have a set schedule. I think from Sky Harbor it 11:59 is the latest trip to LA. Good to look up their schedule on the app or online.
Mine arrived at almost 1am
I've taken this bus before and when it's running late it will notify you but for the most part it's on time or early.
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