Two are adults. Danielle will be 18 this year I think . Haerin next year. I think hyein is only exception because she is still at start of teen years. But she was a child model I read and they can target her audience.. That's teenagers. Schedule can be managed under labour law.
18 is a minor in south korea, so they're still subjected to the 35 hour work week, with 40 hours max if you get special permission from the government. They're also subjected to the no working after 10pm rule without special permission granted, and from what we've seen since that law has been passed with minors leaving award shows early they haven't been giving idols a pass. This is good given the fact these laws were passed after multiple suicides of those who debuted extremely early in the industry
To explain why the child actress had a different schedule, it's because these laws are very very recent. Mid 2020 or something recent, this explains why they didn't farm CFs during promotion. Promotion period ate all of the time as they're not just recording music and choreo practice, they do radio shows and other live promotions.