I don't think in terms of "seatwork" when I plan my kids' days, I think in terms of "structured learning time." Structured learning time includes anything I tell my kids to learn or practice: worksheets, assigned reading, science labs, PE, field trips, learning new life skills, handwriting, drawing a diagram, writing in a journal, history, read whatever you want for 30 minutes, brainstorming for a writing assignment, art, computer games to reinforce skills, filling in a map, learning a song, and so on.
While it seems to me that it would be more efficient to sit down and get all the workbooky and reading stuff out of the way first and then move onto all of the hands on projects. My kids do best with a Charlotte Mason approach with a lot of short and varied lessons. I try to mix PE, science labs and demos, creative activities, read alouds while drawing or playing with pattern blocks, and hands-on activities in with what I consider seatwork (workbooks, assigned reading, math, and writing.)
I reserve the afternoons for classes, pulling out art supplies, fun read alouds, free reading, teaching life skills like following recipes, going to the library, playing music, lego building, and other fun, informal learning activities.