yes it does. the endtime for hydra is staggered to ease server load (or something along those lines) so the clans you're up against might not have their hydra reset at the same time as yours does. to avoid any issues that could cause, hydra clash ends when the first resets begin and the next one doesn't start until after all the resets are completed. hence the 6 hour dead zone between each clash.

i

First time to get 3rd best chest on Hydra Hard.  This is when it is worth all the time and effort.  

Can Mischief deflect AoE damage?

Only if the attack targets him first, such as with hurndig 

I can use aoe raw damage and debuffs to target Mischief as long as he is secondary?

Correct. That's pretty commonly how people take him out, if they don't have Hex. Champs like Husk work very well, and so does HP Burn.

Does Mischief have a 1 in 3 chance of returning to the active battle after being devoured?

The higher the level of Hydra you are fighting, the more likely you are to to get a replacement head that is different than the one you just killed.

The lower the level of Hydra you are fighting, the more likely you are to get the same head back.

I do not know the percentages.  Not sure they have been published.       

so  I personally only run  NORMAL and HARD Hydra  and love the rewards

basically the  most important thing for all my runs is HP BURN = soimpactful on total damage for  my AUTO team/random builds

My roster is composed manly of supports, just recently i got a Trunda and still didnt figure how to make her work. But i can do 600m points+ on brutal with a slow steady team of 2 emics and dont worry about getting eaten. My only dps in this team is grazzur, i have a venus for blight and debuffs, archer for dec spd and taunt, 2 emics with perfect sync to never let unkillable and taunt wear off and shamael to make sure torment doesnt kill my run. My shamael hits like a wet noodle and graazur dmg is good, but capped, even if it cycles fast cuz of the Emics. The team has high res, to avoid taunts, but both Emics have the highest res (not that high cuz graazur gives inc res), as they are the mischief tank.  I still didnt figure out how to optimize it better with my roster but for now it works. If you have a way to cycle taunts, it can really really help u if you have a low dps team