If Game Time is a +0% modifier, then Real Time reasonably is too.
Real Time +0%
If it usually has a certain number of uses per day, then it instead gets that number of uses per real hour. If it usually has a certain number of uses per week, it instead gets that many uses per session.
Once per scene is like Takes Recharge defined in meta-terms rather than in-game terms. A scene is probably equivalent to one hour of game-time at -20%.
Once per adventure is like Limited Use 1 per 1-4 sessions. So that's like an ability that's usable 1/month in game time but with the Real Time modifier.
So assuming an ability with unlimited uses:
- Once Per Scene is -20% [Takes Recharge -20% and Real Time +0%]
- Once Per Session is -75% [Accessibility (1 day a week) -35%, Limited Use (1/day) -40% and Real Time +0%.]
- Once per Adventure is -80% [Accessibility (1 day a month) -40%, Limited Use (1/day) -40% and Real Time +0%]