Advice
It's hard to say "no." Especially in a work setting. Years of conditioning have led us to struggle with an irrational fear of disappointing our boss or co-workers.
"Can you jump on a quick call?"
"Can you join a meeting today at 1pm?"
Boundaries are important. Your work rhythm is important. Context switching is the progress killer. Saying "no" is not something we should fear.
Of course, you don't have to feel guilting by actually using "no." You could always try something like: "I would love to! I'm looking forward to speaking to you more about this but my time is spoken for today. Is there another time this week we could get together?"
That's a "no" without even a negative phrase. You have taken ownership of your time and energy while still being accommodating to your co-worker/boss.
Relevance for today
Work/Life separation has never been more of a challenge since the start of the great WFH migration of 2020. We are working more hours now than before the pandemic began. Just because our laptops phones are now always within arms reach does not mean we have to grab them. Take your time not working as seriously as you take the time you are. Work is important. It's necessary. But it will never be important as your life.