We start school around 8, then if we have someplace to go, we stop school, do what we need to do then, resume when we get home. We just work on it until we are finished, taking breaks for doctor's appointments, field trips, piano lessons, etc.
On days we are able to stay home and at the school table all day, we're done around lunch time, but on days we have lots of outside activities or errands, it's not uncommon for me to be teaching until bedtime to make up for the time we lost.
Sometimes I'm just too tired to do it all in one day, so we'll double up on lessons through the week as needed.