I am a big, big fan of protecting time in your schedule. I live and die by my Google calendar because I can always access it, but on that calendar, you’ll find more than appointments.
There are two kinds of scheduling – appointment and defensive. Appointment scheduling is pretty self-explanatory – you have somewhere to be at a certain time, and so you put it in your calendar. These are the kinds of things that people usually use their calendar/schedule/planner for, and of course, it’s useful. It gets you to where you need to be when you need to be there!
But defensive scheduling is a little different. It’s about protecting time, rather than filling it up. You put something on your calendar so you WON’T give that time away to someone/something else. You claim your time before someone else does.