A Treasury bill pays you back on a date. You can look up a yield for that maturity on a day the Treasury publishes the curve. When the bill matures, the experiment is over. You have cash again, and you have to decide once more.
A saving habit is the decision to keep doing that, or to keep leaving money in a deposit account, on ordinary months when nobody is writing about yields. The habit is not improved by a clever entry point. It is improved by still being there after the yield has fallen and the articles have moved on.