I find it funny how much time is spent talking about MC aging as if the game is going to go for a few decades where it might become relevant. Right now his life is 6 hours shorter from Lucia's time pauses? Is there going to be some epilog with him and Meri living happily ever after in the year 2376?
Based on a conversation in the "normal" path, I would guess Lucia's life span might have been "compressed" (I won't say shortened 'cause she's not losing her lifespan, she's just using it while others aren't) on a magnitude of months, maybe even close to a year, since her powers manifested. And while he may be slightly comically paranoid about his own lifespan, he seems genuinely concerned for hers, and not entirely without reason.
But otherwise yea, you're probably right. Maybe 8-10 hours on the normal path, 6-8 on the manipulation path. Feels kinda like the McCoy teleportation gag Jdor did with Evelyn -- it just happens to him more, so the joke is starting to age a bit for some.