Sorry if this has already been address but I couldn't find any info on this.

I just added a Vertex 3 SSD to the on my 2011 mini using it as a boot drive and still have the existing 500gb HHD installed.
I read that I should DISABLE "Put hard disk to sleep when possible" for garbage collection to work overnight.
What about "Computer Sleep"?
When the Computer sleeps does this put the disk to sleep as well.

If the computer goes to sleep, the drives spin down, yes.

Thought so.

So I'll set my Computer Sleep to never.

So Is there an app or terminal command that I can use to selectively choose only standard hard to sleep when possible?

why would you want your HDD to standby?

i hate having to wait for HDs to spin up when trying to access it.

You've got an SSD so no "spinning down". Also if the computer does to to sleep you wont have the garbage collection do it's work. That put disk to sleep is to spin down the HDD to save on battery life when you aren't accessing the HDD for an extended period of time. Kind of unnecessary for an SSD.