Lets face it:
3 more sec on DA isnt going to change anything at all.
Apart from tankhealing where DA is being refreshed and used all the time anyway, DA is pretty much useless on all our heals.
IF a raidmemeber apart from the tank gets hit (not talking about aoe here), its either a random hit or the tank wasnt doing his/her job.
In either case DA is pretty much wasted because if its a random hit DA wont get used, and if it constant heavy damg on a heal or dd, somebody is doing somethng wrong in the first place, and Da will renew itself because you have to chinheal that person.
Even PoH DA isnt really usefull because most of the time DA isnt used because the aoe damg already happened BEFORE you cast PoH to healthe group.
For DA to be really usefull it needs to be 20 to 30 sek at least.