I can't speak to this particular situation but it's worth noting that last-minute-just-before-polling-begins updates are the norm and happen pretty much every election.
In/around my hometown, for example, the voting machines are "securely" stored in between elections, until just before an election, when they get 'em out to set them up, test them, etc.
Whether they installed updates an hour before an electiion or two weeks before an election, it can still be made to sound "fishy" by anyone who wants it to.
"Why were they installing a so-called 'update' an hour before the polls open?" versus "Why were they installing so-called 'updates' on the voting machines two weeks before the election?"
Obviously, they were installing hacked firmware in either case, right?