The updates happen in order of age of previous map & usage. If a map hasn't had an update for a while, it'll be queued as the next to update.
If a map has been used more than other maps, it'll be queued first to update.
If a map has not be used at all, it won't be updated daily, maybe once every few days, depending on the game.
At the bottom of the list of maps, there is a link to "currently running map updates" which will show you when the maps updated last. Some games only take a few minutes to update, some take a few days.