我搞懂了。

Rule: fixed rate never change, inflation rate changes every six months. 

4/15/2022 issued bond, the composite rate is 7.12%

+ 6 months: 10/15/2022 the rate reset, that rate was 9.62%

+ 6 months: 4/15/2023 the rate resets, the rate was 6.89% - 0.40% = 6.49% (because in april the fixed rate was 0.40% which the 4/2022 bond won't enjoy)

So in 10/15/2023, the rate will go down to 4.30%-0.90% (fixed)= 3.4%.  That's the time to withdrawal, assuming CD rate is still 5%.