Time management

When planning our days, how do you recommend we accurately estimate our time and manage our business tasks (other than coaching appointments) and calendar when we don’t exactly know how long certain tasks will take? I enjoy the feeling of having my days perfectly planned with tasks and specific times on my calendar, but I’m finding myself consistently ambitious with the number of tasks I try fit in.

Current model:
T: I don’t know how to manage my time. Can’t get anything done.
F: Defeated, frustrated, impatient, lack focus.
A: Uninspired.
R: Low quality work, lack motivation in my business.

Desired model:
T: I’m learning to manage my time around new tasks. As with many other things, it may take some time but I’ll get it.
F: More excited, decisive, and energized.
A: Inspired action.
R: Better quality and more enjoyable work.

Thank you!