^^^^^^
Well I Guess in State-Level and Local-Level elections, it would be up to that jurisdiction, but Presidential Elections I am not sure if early voting is constitutional...
It likely is unconstitutional at least for Presidential Elections
The Congress may determine the Time of choosing the Electors, and the Day on which they shall give their Votes; which Day shall be the same throughout the United States.
But for everything else.. I think its constitutional...
so to sum it up for me.. unsure lol
edit: Even the wording of the part of the constitution I posted confused me... Does it only mean the Presidential ELECTORS? 
Yes, I believe it only refers to electors. When the constitution was ratified, the framers didn't expect the popular vote to determine the winner of the electoral votes. Instead, they thought that the electors, who were to be chosen based on merit, should take the popular into account, but not necessarily go along with it.
Poll
