Happy 4th of July.
While it's an American holiday, its impact reaches other countries. Especially in ecommerce where promotions might be available to others (e.g. customer in Canada taking advantage of your 4th of July coupon).
Seen this way, holidays give you a reason to have a promotion and an easy marketing hook. Announce a 4th of July sale and everyone nods their head. Announce a 14th of July sale and some US customers might be confused and think you added an extra '1' to the date.
(July 14th is the French National Celebration)
But there's nothing stopping you from creating your own special promotion days. Amazon did it. Target, Walmart, and others copied them.
Look at your promotion calendar to see if there are any holidays that make sense to have promotions around.
Eric Davis
P.S. Also consider your customers. If there are fan bases or popular dates among your customers, there might be more relevant dates. e.g. if you sell comics, Stan Lee's birthday could be a nice wrap-up to the year.
Is one flavor better at keeping customers?
Compare how your variants perform to find the ones that keep customers buying over and over again.