Kumon Class in Japan

Hi! Does anyone here in Japan send their kids to Kumon?

I recently enrolled my 7-year-old in Kumon for Japanese language. It’s only been a few sessions so far. The class is supposed to be 30 minutes, twice a week, but my kid has only been there about 20–23 minutes each time.

Is that normal?

Do they have a set amount of work planned per session? Once the kids finish their worksheets, are they allowed to leave even if the full 30 minutes isn’t up? Or are they usually supposed to keep working until the time is over?

Would love to hear how it works for others. Thanks!