I do both. I plan 12 weeks/3 months of work (1 term) and give us 4 months to complete it. Our terms are Sept. – Dec., Jan. – Apr., May – Aug. each term we have 4 weeks off and I don’t schedule it. It might be a day here and there or a chunk at once.
ETA – I have always scheduled by terms, but have also used a 3 wk on/1 wk off and a 6 wk on/2 wk off schedule. Those worked, but were more rigid than I like. I block off any definite a right away like 2-3 wks at Christmas, etc.
I’m planning on 6w on 1 off,, with 6 weeks off from thanksgiving to Christmas and 6 off for “summer” I put that is quote because we will get our first 2, 12w terms done before Christmas break. Meaning our summer will be 1/2 or April and all of may. We are in floridas and I would much rather have nice wether off and hot sticky summer inside for school.