Hmm...Interesting.
8 hours is still shorter and cost less than the 12 hours I used to run it (recommended for Baquacil), but 4 hours doesn't really give me a warm and fuzzy feeling either. While my pool is in the sun pretty much all day, I have a backdrop of woods just outside the fence line, just a few feet away. I get leaves in the fall and cottonwood seed (and what look like buck-eye flowers) in the spring.
Perhaps I'll experiment with runtimes, but on the other hand I like to have the pump on while the pool is in use and I don't want to overriding the timer each I go for a swim. Electricity cost is not as much of a concern it was in years past, due to our recently installed solar panels.