Why not? Once a day. What's wrong with that? Or every three hours, it can be determined whenever. It can be similar to the STV arena that is dead.
This solves two things, and can bring fun to the game.
1.) More world pvp. You know when the boss spawns? Everyone will be there to participate. Isn't this what Blizzard wanted with world bosses in the first place? They're called WORLD bosses for a reason.
-What about server crashes. Was there any with Galleon? No.
2.) We know when the boss spawns. We don't have to be online all the time, wondering if the boss is going to spawn at 6 am or not.
Edit: And yes I know Sha spawns every 15 mins after it dies or so. I'm suggesting we lengthen the time for a world boss to spawn, but with a set realm time.