I guess with the issues tonight the Challenges modes are bugged, when you complete it in no matter how much of a time you will be awarded with a time of 00:00:01 also they will give you achievements/gold/valor for it.
Proof: Temple of the Jade Serpent @ Alterac Mountains - Community - World of Warcraft
Because it's not possible to do it in a second obviously.
It might get hotfixed really soon or tomorrow so I would start running them and knock out a couple.