For some bizarre reason Slow Time is doing the very opposite of its stated effect.

I've thoroughly checked every plugin I use for any conflicts, Not a single one touches the Slow Time shout or the Slow Time magic effect.

I even did a bit of testing. It would seem that the effect is being applied at the wrong magnitude. The 1st word of the Slow Time shout has a mag of 0.3. However using the sgtm command to compare I found it was applying a mag of 3.0.

The trouble is since the slow time effect is a hard coded effect archetype, there's no way to fiddle with it.

I'm at a loss, any help would be greatly appreciated.

If you don't have many mods, try to disable those, and see if something changes. (Try that on a new save)

I've got about 70 plugins enabled. It'll take some time.

EDIT: Aha! I found the guilty plugin. It was Balanced Magic. Strange though, as it doesn't touch the slow time effect at all. I guess I'll be stuck with vanilla magic for the time being.

At least you found the culprit...