Protect + shell should last 10 minutes and not pull more hate than provoke or taunt.
Shock spike should last 5 minutes
Stygian spike and stoneskin should last 3 minutes.

Also, THM and CON should have like a rnk 25 quest that teaches them an ability that lasts 1 minute (10 minute CD) and doubles the length of these buffs when casted under the effects of this ability.