Professionally, I say very explicitly and almost without emotion:
I have x number of hours of available.
This is what I am going to do today, tomorrow…and this week.
This will not get done by the end of the week.
Let’s get the task completed. I need x, y, and z.
And yet oddly enough, all of us have trouble applying to it to our personal lives, particularly interpersonal relationships. I know that I do.