I thought (and the Rise thread would be a better one to check) that the 1 pm slots you had to be in the park, not necessarily have a park reservation (where in the morning you only need a park reservation). The boarding groups in the afternoon are regularly taking longer to "sell out", quite often past 2 pm. I thought someone in that thread confirmed that if the boarding groups was available after 2 pm you could get a boarding group if you hopped.
They also have at least once now opened up stand-by for Rise at the end of the night (I think it was Sunday) when all the boarding groups were called. It seems now at the end of the day when boarding groups are still left, Cast members are showing people that walk up how to get a boarding group rather than just open up stand by (at least that seems to be the trend since Sunday).
@DCBaker has been following it much better than I, as has
@disneygeek90