Using Treasury Direct For TBills Reinvested

[TripleB]

Treasury Direct is advertised to allow reinvesting of T-Bills/Notes/Bonds upon maturity on an automatic schedule unless canceled.

I initially thought this was a bad idea because TD doesn't allow IRAs, so I can only do this in Taxable accounts, and cash is the most tax-inefficient asset to hold in a taxable account.

However, with the VG Treasury MMF being closed, and with interest rates really low (so virtually no tax-hit will occur), I am considering putting some of my cash in reinvestable T-Bills at TD.

I envision doing this with 30-day T-bills. Has anyone done this? I imagine they don't make new auctions on exactly 30 day increments, so does my money just sit in the 0% C of I account inbetween auctions if there's a delay? That's fine since it's earning practically 0% in TBills anyway.

It appears that TBills are only sold in $100 increments on TD. What happens to money that exceeds the $100? I assume it just falls off and into the C of I account at 0%. However, how about if the C of I account starts to exceed $100? Will it be smart enough to know to put that into TBills? I presume not.

Thus, once interest rates rise, I assume this isn't an automatic operation because at a certain point, I'll have $100 more than I started with, and TD probably won't know to invest that into a TBill. However, once interest rates rise, the VG Treasury MMF will likely re-open so I won't need to use TD for this.