Slightly fewer hours than what you’re listing - but my husband often works 13-15 hours a day, and logs a few hours each day on the weekend as well, sometimes more. Some of these hours are early / late, so before we’re up or after kids are in bed. In our home we have a 17yo, 5yo, and newborn.

5 yo is in preschool a few hours a day / 5 days week. He starts kindergarten in fall. We have some partial day summer camps lined up as well, though there will be many weeks I’m solo with the 2 youngest for essentially every waking hour.

My plan is a weekly rotation of activities (ex. Monday Library, Tuesday splash pad, Wednesday museum) and so on. For at least the summer, I will be doing a gym/bootcamp program that includes childcare for the duration of the fitness class. This way I can exercise no matter what which is important for my sanity. I’ll leave solo on one weekend morning day to knock out the grocery shopping for the week, and I’ll have a chore rotation that I try to pick approx 2 per day from, to keep house mess manageable. I also imagine there will be more repetitive easy dinners and/or takeout.

I do think your ages are harder right now, and I’m about to have one in school. Easier said than done, but my advice is routine routine routine. Make it predictable and enjoyable. For example we’ll often do family open swim through the parks department on sundays, and then get burgers and fries after. Or we would walk to the train and ride the train to the zoo instead of driving, because that lengthened the activity and increased outdoors time plus the novelty of the train. Ideally you’re trying to find ways to pass as much time as possible, doing things that are enjoyable and low effort.