The contract absolutely, positively has to be there yesterday.

Hint 1 of 9:

It's too bad that Bernard can't travel back in time to mail it.

Hint 2 of 9:

But wait!  Hoagie has traveled back in time, and you can give him things.

Hint 3 of 9:

Before you do anything with the letter, you'll still have to find the proper
postage for the 1770's.

Hint 4 of 9:

Weird Ed collects stamps.

Hint 5 of 9:

In fact, he has some Pony Express stamps that you can use.