We can estimate. Assume that the OP needs 8 hours, like most of us do. That means a 9pm bedtime for adequate sleep. The OP mentions that the first call is at 7am. Assuming a 40 hour workweek, with an hour for lunch, that's a 4pm clock-out. This gives OP 5 hours in the evening/afternoon and 2 hours in the morning before work, and an hour for lunch, for a total of 8 hours 'off'. This is a very do-able schedule for morning people. Mixing kiddos into this is not too bad when they are young, but as they turn into teenagers, this is likely to shift towards later hours as the teenagers shift too.

Personally, my natural times are a 8am wake-up and an 11pm bedtime. I need the extra hour and I'm a night-owl. Couple that with a mandatory 8am stand-up and 6pm 'clock-out' time for my job's work schedule. It's ... less than fun in Corporate America.