This AppleScript set the status and status message in iChat depending on what argument is passed and whether the screen saver is running. It is run by cron (for example), take the argument and current time (in local tiemzone) and set the status message. The status is set to away if the screensaver is running, and available if it is not.
The cron settings is for example preferrable the following:
* * * * * osascript /Users/paf/ichatstatus.scpt "Home"
You edit the crontab file by giving the command