Usually during the summer when school is out as I have basically unlimited free time. So I'm always starting new projects, tinkering, ect, and I work more time at my LFS over the summer as opposed to when school is in which means there's always stuff to grab
It's a hobby. There is no such thing as 'done'... but there are periods when I'm more actively changing stuff, and times when all I'm doing is watching, feeding and basic maintenance. Seasonal? Don't know why reefing would be seasonal. It's all temperature controlled, after all
I have always been active its not a hobby where you can stop being active in it. Because if you do it will take months if not years to recover. I am always working on my aquariums and its my main hobby as I learn something new every day of the year.