The way I see a calendar is for events that must happen at a specific time (appointments, birthdays, classes, etc.). To-dos may happen at any time. For example, I workout after lunch. But I don’t always eat lunch at the same time for the same duration. My workout may happen at 1pm or 3pm. Why do I need to schedule it at a fixed time?
Instead of scheduling todos, we could just timeblock them, and only allot N hours per day to tasks.
I just have an X amount of time in my week outside of my varying weekly study schedule so I plug things in and allocate with a lot of buffers in-between to not be too tight.
It’s important to not be too harsh on yourself if you didn’t manage to do something. Just move it over to next week free block and re-adjust it on your next planning session on Sunday.
If it is something extra important with a deadline, mark it with a couple of exclamation marks. You can then at the end of week also review your progress with your longer-term goals. Voila! Works!