Homeschooling at our house is every day, every month. Of course, we are unschoolers and the kids are still young, but the idea can really apply to homeschoolers of every stripe. Basically, I feel that we can spread the learning out over the whole year. We take restful/lazy days after a weekend away, or the day after gymnastics and a trip to town, sick days and beautiful days. Regular events, (swimming lessons included) plus my work schedule, keep a natural rhythm to the week.
Are you the type who needs the daily structure because it keeps you in a good groove? Then I would definitely do less "schoolwork" each day and stretch it for the entire year, including summer. If you can more or less easily pick up after a long break, then by all means, take the summer off. It's never a break from learning, if you see it that way, just a break from desk (or couch) work.
Changing focus can be helpful if you still want to be more formal than we are, just center subjects onto hands-on outdoorsy nature and science stuff. When we go for walks in the woods, we take "science backpacks" with colored pencils, sketch books, magnifying glasses, measuring tools, and I'll carry binoculars and field guides. I let the girls lead, but you can be more purposeful, too. After all, it's what real scientists do: some fieldwork followed by compiling data.
Have a glorious summer!