"You make food on Monday."
Translation:Du laver mad på mandag.
"Du laver mad om mandagen" would mean, you regulary/always cook on Monday. If you talk on Sunday about who is going to cook next Monday, it is "på mandag". It is tricky, because "på" is only used for weekdays in the future! -- på mandag (e.g. next Monday), but "i weekenden" (next weekend), "i morgen" (tomorrow) and "i næste uge" (next week).
I translated this sentence "Du laver mad paa mandag" and it said I was almost correct that the correct answer should be "I laver mad paa mandag". How is one to know if we should translate "you" as plural "I" or singular "du"? The translation above says "du", but the program said "I". It's a bit confusing.