Don't forget that Afilia Sherrys (and Asterisk too IIRC) is open from 5 PM to 5 AM, so that means girls like Karen, Kurumi, Maho, Miku, Laura and Yukafin have very irregular sleeping patterns as they work nights. I guess some of their tweets are posted during their breaks or when they get off from work. I assume the girls don't have to work the night shift if they have a performance the next day, but even so, it might be hard to adapt and they're likely to lose hours of sleep.