Very nice, thanks tboehrer :]
For those who want to use the W3 Date/Time format as Pamel suggested, I've saved you the (little) trouble so you can just paste this into the format:
%Y-%M-%DT$H:$M:$S$T
Edit:
you can also convert the older PLAY_DATE and PLAY_TIME tags to this format, as tboehrer pointed, using the Masstagger's "Format value from other fields"; use the following:
20$right(%play_date%,2)-$substr(%play_date%,3,4)-$left(%play_date%,2)T$left(%play_time%,2):$substr(%play_time%,3,4):$right(%play_time%,2)+08:00
Remember to replace the "+08:00" with whatever timezone $T gives you
Edit 2 (yeah I know; bored and nothing better to do..):
Formatting string writers, you can parse this into a nicer display
(namely, 2004-04-15T21:02:05+08:00 -> 2004.04.15 9:02:05 PM) with the following:
$if(%play_stamp%,
$left(%play_stamp%,4).
$substr(%play_stamp%,6,7).
$substr(%play_stamp%,9,10)$tab()
$if($greater($substr(%play_stamp%,12,13),12),
$sub($substr(%play_stamp%,12,13),12),
$if($strcmp($substr(%play_stamp%,12,13),00),12,
$num($substr(%play_stamp%,12,13),1)))
$substr(%play_stamp%,14,19)
$if($greater($substr(%play_stamp%,12,13),11), PM, AM))
What's nice about this one is that you can easily change the separaters if you don't like '-' (I find '.' the most visually appealing)
Edit 3: small fix in above title formatting (12 PM/AM)