Validity of letter of undertaking

The manufacturuer export can export the excisable goods by furnishing UT1 (under taking in lieu of bond) and as per law the UT1 shall be valied for 'twelve calendar months'. If is confusing that whether the validity is April to March or January to December or twelve months from the month in which UT1 is executed.

Experts are requested to give their opinion asap.

Thanks in advance.