We disclose the interest rate and the APY for Certificates with maturities less than one year. If the annual pertentage yield is based on one year and the certificate is for 6 months, compounded at maturity and is not renewed, why disclose a APY calculated on 365 days? Do we have to disclose the APY on terms less than one year?

Because ALL consumer deposit accounts are expressed on an annual term. This way interest bearing accounts can have an "apple to apple" comparison.

Yes, you must disclose the APY for ALL terms.