How would you spend it? If miraculously, there was unscheduled time -- what could you accomplish?
Now the important question is: Why aren't you doing that right now? Why isn't it a priority to fit it into your schedule today? Do you really want to accomplish that something? Find the time. Make it an actual priority....today. Don't wait until someday. Don't let yourself fall pray to the "someday" vision.
If it's not important to you but you think you "should", maybe you "should" let it go. If it's honestly important to you -- get to work!