Please explain?
You have margin option added to your account. Simple to do.
We will use this week's 26-week bill as an example for 1k.
If you had 26-week bill maturing this week with Fidelity and AR on you do nothing.
With Schwab you turn off AR on the bill maturing this week.
You buy the 26-week bill today on margin. Its settlement date (money due) is Thursday.
The 26-week bill you turn AR off on also matures on Thursday.
The money for the purchase today (due Thursday) will come from the bill maturing on Thursday.
Works the same as AR but more work.
I am terrible at explaining so ask away for the parts that are not clear.