You can get some idea about meaning of 'month' in airline ticket validity from CX online reservation.

HND-HKG 15Oct
HKG-HND 15Nov
-> 1 month, V class fare applied (V class fare is defined as one month. not 30days/31days/...)

HND-HKG 15Nov
HKG-HND 15Dec
-> 1 month, V class fare applied

HND-HKG 15Nov
HKG-HND 16Dec
->1 month + 1 day, V class fare can't be applied.

HND-HKG 12Nov
HKG-HND 26Nov
-> 14 days, S class fare applied.