Mine was always this:
Manager: How long will this take?
Me: 14 days
Manager: So it will be done in 2 weeks?
Me: No, it will be done after I’ve had 14 days of time to work on it.
Manager: What’s the difference?
Me: Am I still going to have random support escalations and will we keep having random meetings in those 2 weeks?
Manager: Yes.
Me: All those interruptions are me NOT working on the task. So it will be done in 14 days plus all the interruptions.
Manager: But this is very important!
Me: Can you then ensure I’m left alone to focus on this?
Manager: No.
Me: …