You're right - the 3 - 6 pm hours are our bewitching hours too. I do mine right after I do morning drop off - around 8 am. When my daughter wasn't in MDO (she's now 3), I took her with me on walks or set her up with paint or playdough so I could get at least 30 minutes in.
Also, right after bed time is a good time to do yoga, ab workouts, things that don't make much noise and don't require you to get all hyped up before bed are good for me.
Best of luck! I know it's hard - I work at home and work out in or around home!