Ooooh, honey.... I feel for ya. I haven't had to transition anyone for a while, but I remember!!
I would give it at least a month, longer if he/she is only part time or occasional. I find part timers can take 6 weeks or longer to settle in. That being said; it should at least start to get better after a couple of weeks.
In the meantime- got earplugs? (kidding!!)