OTA priming improvements

* make cache timeout hours and not seconds
* allow checking cache without generating it
* provide better completion messages
* allow specifying usernames as well as user_ids

@czue @NoahCarnahan 
i see it's irrelevant now based on how/where it's called, but might be worth fixing in case anyone else tries to use this method and gets confused. (alternatively could add an underscore to the front of the method name)