During the day normal people buy the songs they like. AT night stans of artists plan download nights/days and sit around gifting songs and stuff.
nnnnn sis only the kats will be doing that for DH and it makes no difference. If Happy is destined to hit #1 it will. And it will. Probably sooner than you think. The DH video will only bolster Katy's song for a week and by then Happy will be caught up on radio and even further ahead in sales.