Wish I had an easy answer!
That's a toughie. However, I applaud you for wanting to fit it all in there. You know what "they" say...make it an appointment and keep it like you would any other.
So...let's see. Can you walk on your lunch hour? Do you have an office? I work with someone who just came back from maternity leave and she just shuts her door at lunch time and does pilates and works with a fitness ball for half an hour. Could you keep a couple of weights around and do some exercises during lunch or breaks?
No, tying your daughter in her room is not an option. How to get her to stay in bed is a whole other issue for which this isn't the time or place, but, given that she is going to get up anyway, could you explain to her that the next half hour is "Mommy time" and that you have to do your "homework"? Maybe agree to let her lie on the couch while you do your exercise and tell her that her job is to either (a) be perfectly quiet or (b) cheer you on (whichever seems more reasonable)? Or is there something she could entertain herself with in her room if she's not ready to go to sleep?
My only other thought is to move whenever you can find time to. I have been known to put on the iPod the day before Thanksgiving and dance at the stove while making 10 loaves worth of stuffing...about an hour and a half. Can you do bicep curls while supervising homework? What about weekends; do you have some time there to do an hour block? Would your kids exercise with you during your "together" time?
Sadly, you can't put extra hours in the day, and you can't stay up all night. But there has to be some time, if you're creative. Good luck!
And now that you don't have to be perfect, you can be good.