I upload whenever I have the material. I am not really selling for THIS holiday, but for every similar holiday in the future.
Typically I go to some celebration (New Year's Eve, Corpus Cristi, whatever) and capture it the best I can. I then edit all the material, which takes me several days. At that point, I have missed the news cycle (let alone advertising cycle) for this year. But now my stuff is there for next year, whenever a buyer decides to look for it -- and every year after that.
Sure enough, Corpus Cristi is a big deal here in South America. I shot a couple hundred images back in 2013 at one of the celebrations. My first sale on those images was in 2014, and every year in May/June I see them coming up again.
Doesn't make me rich, but those sales here and there for this and that is basically what stock photo market is all about...