Biden only gets lucky in PA a full day after that if you look at vote share per batch, well after in-person votes are counted, and the later you go, the luckier he gets.
The pattern is the same in every swing state except Arizona, and in Virginia as well. If you plot out Edison data that has vote count updates, in "normal" states (both Biden and Trump dominant), things are chaotic initially (when in-person votes are counted) and then they settle to a certain GOP/DEM ratio, with a very slow drift towards GOP, presumably because rural votes take longer to show up. In the swing states you observe the same initial chaos, and the same slight initial drift towards GOP, but then Biden starts to get very lucky indeed, and his luck improves as time goes on.
To be fair, this could just be artifact of how votes are counted, in which case I'd like to see what could lead to such a pattern _only_ in the swing states. Or this could be evidence of vote rigging by all means necessary. No matter which side you're on, this should be looked into.