Short answer: I can do a mix in about 6 hours, but if you want my best work, give me 3 days.

Long answer: If you tell me "We need this mix for the label by tomorrow", in all honesty, that puts me in fast mode and I won't try as many creative things as I would normally, and sure, your mix will be balanced, but it's possible it could have sounded better.

Why some engineers brag about how quick they can turn out a mix, is honestly beyond my scope of understanding.