I agree with Mr Red that the sequence year-month-day-hour-minute-second makes a lot of sense, since it puts the largest units farthest to the left, the same way we do with pounds, shillings, and pence; gallons and quarts; or any other kind of measurement I know of.

In fact, I use a computer program that formats date and time exactly that way so that records can be easily sorted into chronological order according to when they were generated.