it was stated in magazine scans where they interviewed the cast members. I was also *sort of* friends with Niwa Mikiho (GoseiYellow) during my time in Tokyo thanks to her good memory of remembering new faces and that radio show where fans were allowed to go to the studio to watch every Sunday... back to the topic, she has mentioned waking up at such times in person and even on her blog. I think I've seen a few other Sentai alumni who said so on their blogs as well.
EDIT: Right, Hikari and Kagura's actors are still in school. Tokatti and Mio's actors... well, let's say it's not common to see young actors/actresses in Japan going to college.