SetCooldown questions

[Ailae]

Hey all.

Is it possible to specify if some time has already passed when using SetCooldown?

I have a button you see, which I use to cast one of two buffs. I want to use the cooldown model as a timer to see how long is remaining. But I can't make the cooldown model reflect if time has already passed, like if I login and the buff is at 30 seconds and the total duration of it is 60 seconds, I'd like it to start at already half-filled.

Is this even possible? I noticed actionbars can use GetActionCooldown, but that only seems to work if you're using one of the 120 action-ids.

Any thoughts?

Thanks in advance.