Question: I'm looking at the PayPal `IPN docs`, and it says the `datetime` stamps of their strings are formatted as:

```
HH:MM:SS DD Mmm YY, YYYY PST

```

So year is specified twice?

Once in double digits, and another with 4 digits? 

This looks bizarre.

Answer: 
Complete date plus hours, minutes, seconds and a decimal fraction of a
second
 YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00)
Where TZD = time zone designator (Z or +hh:mm or -hh:mm)

Example
1994-11-05T08:15:30-05:00 corresponds to November 5, 1994, 8:15:30 am, US Eastern Standard Time.

1994-11-05T13:15:30Z corresponds to the same instant.

<https://www.w3.org/TR/NOTE-datetime>
Actually, I think the right format is: yyyy-MM-ddTHH:MM:ssZ

The case is important.