Another 2 get taken for eating/commuting if you live close to work, let's say you spend another 1-2 per day taking care of your school-aged children, so now you're down to 20-30 hours a week. Let's say you spend another 5 of those doing social things, that's 15-25 hours a week. Subtract another 5 to deal with errands... 10-20. Some more of that will likely go towards your spouse.

That means you get something closer to 500-1000 hours a year. Perhaps you can get more if you carefully prune.

That's enough to do stuff, not enough to accomplish a second career.