I just counted on the calendar and Hanukkah is NOT 280 days from Nisan 1 and thus NOT the birthday of a child conceived on Nisan 14. At most it is 262 days from Nisan 1 the earliest would be 261 days. The 8th day would be at best 268 at most 270 days. Using the religious calendar as a pregnancy calendar the birth would be at best Tevet 13 the latest would be Tevet 15. The average or normal being Tevet 14.
 
Since Hanukkah is a MAN created feast, not God created, it would make sense that it would NOT fit with the pregnancy calendar.
 
Paul