Sounds like a good plan to me. Just allow plenty of time for ACH transfers so you don't end up losing some of your interest to wire fees!
Note that you could put your money into a money market fund like VMFXX for the week or two between the treasury's maturity and the down payment date.
Also bear in mind that a national debt default could delay repayment and cause a seizure in money market funds, although most observers consider that to be an outlier risk. If that did occur, it would probably be in your financial interest for the house deal to fall through due to unforeseen circumstances.