TimePart is an easy to use and free Adium script that will help you send the current local time and date, formatted as set in the International pane of System Preferences (for non-Unicode formats, only; unfortunately).
Examples (using Australian settings): %_TimePart{short} => 27/11/04 %_TimePart{weekday} => Saturday %_TimePart{full} => Saturday, 27 November 2004 8:13:57 PM
NOTE: "%_TimePart{help}" gives a full list of supported commands, and shows the results they give.