I'd love Protect & Shell to be like 10 or 15 minutes because it's a hassle to try to gather your party members in one spot to rebuff them every 5 minutes. (You know, it's like herding cats!) 30 mins, however, is overkill in my opinion. I'll be jobless in the party because I won't have much duty to do if Pro&Shell stays for too long.

Shock Spikes & Stoneskin, on the other hands, are fine as they are, since Stoneskin breaks quickly from the damage absorbed anyway. And Shock Spikes, I usually just have to worry about casting it on meleeing members, so it's not hard to throw the Spikes on them while they're fighting an enemy, without worrying about gathering everyone together for the buff.