MMO's are forced to bend the rules of logic or immersion in some cases. This is one of them. Merchants will be awake and open 24/7
LOL, yeah it would be cool to have different vendors for different hours of the day =)
As a longtime Morrowind player who only picked up Skyrim a few months ago, I have to say that the daily schedules are really annnoying. Immersive, certainly - but the wait function is so damn slow that I welcome ESO's return to static NPC's.