Minimum power for an aspect from magic = 3 shifts. Possibly plus additional shifts for duration - though, as per here, houseruling the default duration to something more than just one exchange is a very plausible houserule.
Yeah, while it's not RAW, I like the idea of using the time increments chart* along with a "what makes sense" approach to temporary aspect duration. In play, most tend to fall in one of four time categories: fragile / one exchange; until resisted / removed (less than a scene); scene; and consequences. That said, the changeling PC in my game did pick up a curse which will last years.
*Roughly what consequences are...temporary aspects around for longer periods of time based on severity / shifts.