Hello Dominik,

The Org mode documentation says that Org mode uses ISO time
stamps. Although Org mode date/time format is inspired by ISO, it is not
fully compliant, see for instance http://fr.wikipedia.org/wiki/ISO_8601
on ISO date and time format.

I corrected the documentation and attached a patch.

FYI, in ISO date/time format looks like this:

2009-09-18T07:16

while Org mode is like that

<2009-09-18 ven. 07:16>

(this timestamp was generated by `C-c .' on my machine, `ven.' means
`Fri' in French).

Intervals and are supported by ISO, with a `/' separator, while org uses
a `-' separator which is ambiguous in ISO (+ or - are used for the time
zone). 

ISO also supports intervals specified with a duration with the `P'
seperator, such intervals may be defined relative to begin date or
end date

ISO also supports repetitions with the `R' separator, while Org uses a
`+' separator.

If ever you want to implement ISO 8601 format into Org, I suggests that
ISO8601 timesamps/time interval are encapsulated into `<I' and `>' where
the leading `I' would help Org to disambiguate from native Org mode
format (although in case where `T', `P' or `R' is used, it is possible
to guess it's an ISO format.

So the example I gave would be:

<I2009-09-18T07:16>

There could also be some relaxed ISO using an `i' prefix like this:

<i2009-09-18T07:16(ven.)>

where the day short name (eg. `ven.') is shown between backets, as it is
cool to have this information. Relaxed ISO would just strip _anything_
between brackets before interpreting the timestamp, so it would be quite
robust to locale stuff (like `ven.'  instead of `Fri'). 

Very best regards,

   Vincent.

PS: I may contribute on this, if you wish.