There may be a misunderstanding
The idea is to keep your time-specific (what I believe you're referring to as "pre-schedules") events and anything that must be done that day on the calendar.
The idea behind this is that so many people write a lot of "to-do todays" on their calendars, or decide that they'll do XYZ on a certain day, and that leads to tension as it becomes clear that life has other ideas on that day...!
So next actions go on lists to be done as soon as you can get to them, and the calendar is reserved for actual day- or time-specific information...
Hope that helps!