Nope not strict, just a mom who knows best for her children. If you look at the research, kids need at least 8-10 hours during this age range and little bit more once they're in their teen years. Their bodies need this just to stay healthy.
Of course, they think now that they're a little bit older, they don't need as much sleep but for them to perform at school everyday, they need their rest. Especially since after school they have activities. They need that amount of sleep so they can work/play at top performance.
On the weekends you can be a little lax but once your body is used to a specific bedtime, you tend to get tired around that time anyway. You may push through and ignore the signals but you're tired.
I would probably let midnight slide on a Friday but personally, if me and my family are not doing on Saturday that has us up late, I try to stick with the same bedtimes. That's so we'll be rested and not so tired Sunday morning and because I think it's rude to sleep in church which I see alot of teens doing. But that's just my opinion.