xkcd #3232: Countdown Standard
Title text:
Anyone who is caught counting 'three ... two ... one ... zero ... GO!' will be punished with a lifetime of eating only ISO standard food samples.
Transcript:
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Source: https://xkcd.com/3232/
The day of the week shouldn't matter, it's either the Sunday that is coming up next or the one exactly a week after it. "This Sunday" should be the upcoming one and "Next Sunday" should be the one after. Doesn't matter if it's this week, next week or in two weeks.