@Pen-y-gors - I can't decide whether you deserve an upvote or downvote...
For recipes, think significant figures, "about 220g" is 2 s.f., so from 210g - 230g, or specify the error margin: 228 ±15g. Changing units depending on whether you are working on "natural", "human" needs or calculations is a bit crazy,
"My lounge is 10' x 15', how many floor tiles will I need?"
"Uh, can you re-measure in metric?"
But then you redeem yourself with a pint of beer, 20 fl. oz.
Getting back to time, another advantage of YYYY-MM-DD is that there is no confusion over which format is being used (now someone is going to tell me there is a country using YYYY-DD-MM, to mess things up).