If Lee caught wind earlier of how fast the AotP was moving to meet his PA offensive, would it have been possible for him to order a concentration at Gettysburg while Longstreet was in Hagerstown? He can't come down the Chambersburg Pike on day one, since Hill is already on that route, and coming up the Hagerstown road would let him outflank Union I Corps on Day One, with the possible effect of all three ANV corps converging on I and XI Union (demi-)Corps on Day One and destroying them (they practically were OTL, after all).
If I and XI Corps were mostly knocked out on Day One, would Hancock still have advised Meade to keep funneling troops into the area south of Gettysburg, or would they have immediately retired to the Pipe Creek Line after one day?