[noppid]

Well, first you have to work out the users timezone if they are a member. So look at $vbulletin->options['hourdiff']

something like

$timestamp = TIMENOW - $vbulletin->options['hourdiff'];

Then you can get the hour with $hourofday = date("G", $timestamp )

Then you can work out the condition.

if ($hourofday == 6) $message = "6AM";
if ($hourofday == 20) $message = "8PM";