I say the same applies to gym memberships, diets, and any other "behavioral change" tied to a date. No need to tie life improvements to milestone dates like New Years (or Lent, etc). I postulate that enduring change doesn't occur overnight and doesn't care about the date -- so start now, keep at it, don't give up.
PS. The same applies to the other 1-day celebratory events: Valentines Day, Birthday, Mother's / Father's Day and even Christmas. Celebrate the moment and the person (as applicable) every day, space it out. It's less expensive than 1-time, all-out blowouts and - more importantly - the person (or persons) will appreciate the longer-term commitment. Space out the love and fellowship throughout the whole year!