This question has been answered by BobRay. See the first response.
var serverTime=[[+server_time]];
$modx->setPlaceholder('server_time', time());
$code = str_replace('[[+server_time]]', time(), $code);
serverTime = [[!getServertime]] * 1000
return time();
nextWeekday = [[!getNextWeekday?nextDay=`Friday`]] * 1000
return strtotime("next $nextDay 00:00 CET") //returns the time of the upcoming defined day at 00:00 CET