This is a generally question of all things scrying... does the casting time and duration of these items follow the same rules as the spell scry? or can you "turn" it on any time and look in it for hours?
If you are referring to a crystal ball, or using the mirror like a crystal ball, AFAIK no you don't have to wait an hour to look at your target in the crystal ball and you can look for hours. You still need the Scry skill however.
