Aw well that is a bit of a shame with your RL, but if that’s how it is there’s not a lot to do about it.
I use Unleash inside the belly on Gorefiend, right as I have topped a spirit and run to catch the newly spawned one, but outside of that I mostly use it purely for the movement speed it grants. I see the healing increase as more of an added benefit to running to my destination faster than an actual tool, because of how weak the heal portion of the spell is. There are moments where you can pop it pre-maturely for an incoming big hit on the group, it just requires the group to be almost topped already. If that is not the case, you’re better off casting another heal.
I agree with Iron Reaver, that boss is just a pain. Just wait until hunters get class trinket and demands to stand at max range……… You might just remove them from your raid frames! 😀