There are a ton of different way to format dates and times. I don't like any of them, so I created my own. I call it UDC. That stands Universal Date Code. With UDC, one can express a point in time anywhere within a 10,000 year period, accurate to within one minute, within just 16 bytes of data, and still be arguably human-readable. The current time at the time of this writing expressed in UDC is 3m0090725d7-1344.
Broken down, that means:3m - the 3rd millennium
009 - the 009th year
07 - the 07th month (July)
25 - the 25th day of the month
d7 - the 7th day of the week, where 1=Sunday and 7=Saturday
1344 - the time expressed on the 24-hour clock, 1344 = 1:44pm.
I have been using this system for over 5 years on everything from academic papers to personal journal entries, to stuff at work and everything in between. I designed/use a fairly comprehensive filesystem for archiving large numbers of images and personal information, where all directories in which such information is relevant, have a UDC prefixed to the beginning of their filenames. This is useful because in my experience, file metadata does not port particularly well across different operating systems or even versions of the same OS. So in sub-directories where the date is the most relevant info - such as directories separated by month - contents can be made to display in that date order always.
Remember the Y2K bug? What I like about UDC is that it can be used for another 6,991 years before UDC would potentially encounter any y2k-style bug. And 6,991 years from now, all it would take to remedy such a bug would be to prefix all UDC dates with a single digit before the m with a 0. And by then I should think humans would have colonized other planets and star systems, such that the 24-hour clock and the 12-month-cycle/365-day calendar year would be irrelevant and no longer in use. But until then, I'm using UDC.