I found a Solid Chest in World of Warcraft and I looted it. After how much time will it respawn so I can check it again?
You are not supposed to camp chests.. The chests in the game (Solid Chest etc) are still in the old world and contain mostly very low-level loot that won't do you any good. In the higher level areas there are no chests at all, so don't waste time with chests.
Also they don't respawn at the exact same spot. There are a number of spots where they can spawn but it's rather unlikely they will re-appear at the same one.
Here is a map of all spawn locations for Solid Chests: http://www.wowhead.com/object=2850