I do maintenance and tinker with my tank every Sunday and most Saturdays as well. Once normal maintenance like checking parameters, changing filter socks, cleaning sump...etc is done, I always find things to tinker with on my tank. I can't help myself. Wouldn't be much of a hobby if all you did was look at the tank.
Some projects I'd spent my extra time working on the tank include adding pneumatic struts to the canopy lid so it lifts itself up, Custom sewn "double" filter socks that are 14" wide and have 2 chambers so they almost never clog, DIY GFO reactor, DIY light diffusers...etc. I can't help myself but spend almost all of my limited free time tinkering with the tank. Since I've got my tank about finished, I'm getting ready to start up a frag tank to open up a whole new side of the hobby! That should keep me busy for the foreseeable future