Okay, let me see if I am getting this straight.
1. It is a spell.
2. It gives a very versatile aspect to tag.
Yeah, that is going to be at least 3 shifts for the tag. Since it is Thaumaturgy, you can easily make it last a whole day for a few shifts of power. And since it is Thaumaturgy, it is easy to avoid stress anyway, so don't worry about that.
Honestly, it seems kind of too good since it is so broad. Maybe if it is restricted to being only usable on things that are sufficiently luck based? Like any skill the character is mediocre (or worse) at, to count as shifts spent for time duration (2 shift time reduction), invoke for effect to find something that can help (you find a hair pin while locked up in a closet), and things like that.
So instead of being a +2 tag, it can make it possible to do something without a penalty or faster.
This would work out really well (and balanced) as a potion. Because that is basically what it is, a potion.