Solve Improbable or Impossible problems... first you need to address what the problem is. I don't see this as "I'm socially incapable, so I want to boost my social skills" I see it as "I want to manipulate this guy into agreeing with me." The goal isn't to raise you skill so you can do what you want with it, the goal is to accomplish X by temporarily increasing/replacing your effective skill.
The Duration and Enhanced Evocation section on 265/266 says that thaumaturgic spells that inflict consequences or temporary aspects on living targets don't have a base duration of "until sunrise." They don't have an intrinsic duration, they happen and they are done. The effect they caused might last just like a normal consequence or temporary aspect.
Disclaimer: I think I'm agreeing with you, Llayne. It makes sense to me, assuming I'm interpreting what you're saying:
"I want to manipulate this guy into agreeing with me." is pretty broad. It could be as short as a singular Lie or as long as an entire social combat.
As far as I'm concerned, if you want to win a social combat with a ritual, you need to put enough shifts in to it to fill all his consequences, assuming a perfect +4 roll and assuming he has a max defense. That's how 'heart explosion' spells work. That's, generally, how you 'take someone out' in a combat.
The improbably/impossible problem has a set Difficulty, usually. You get one shot at it and if you don't put enough shifts in to it, the spell fails.
So, putting 5 shifts in to a skill replacement spell is not good enough to win a social conflict. It may be good to get a single lie or compliment in. That's it. I wouldn't allow you to re-use the same 5 shift skill-replacement spell over and over again for an entire scene.
If your goal (or problem) is to pass off a single lie, than a 5 shift spell *might* be enough. If your goal is to win a social conflict, you're likely to fail with 5 shifts.