Christmas and New Year are short periods (1 or 2 days) of generalized reduction of flow in Stackoverflow. There are a rule for add more 1 or 2 days for grace period? Can we (users) require this rule here?
The week period for promotion means that anyone that is thinking of offering a bounty can calculate if they want to postpone asking it since they'll be out having fun when the bounty ends at Diwali or Sturgis Bike Week or any of the counting system rollover events (a.k.a new year's day) that people love to celebrate around the globe.
One of the nice things about Stack Exchange is that it is worldwide, very inclusive and tries to be open to everyone's time of communication in an equal manner. If anyone wants to avoid a time to issue a bounty, then they have that control today. Why code in some extra cases and have to worry about which dates to include as exceptions when there isn't a problem in the first place.