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The best way to deal with an interruption is by deflecting and redefining it.
(1) Rephrase what the person said, using your own words: «We need to get together to discuss the meeting.»
(2) Then redefine that requirement in a way that favours your schedule: «I will be available today after 3:30pm and from 10 am until 12:00 every other day this week. Why don’t you tell me what 30-minute block of time would work best with your schedule? E-mail me this afternoon and I will respond by the end of the day so we can confirm our engagement.»