You can create an archiveNotification object like this:
$idSite = 7; $period = 'day'; $date = 'today'; $segment = ''; $archiveProcessing = new Piwik_ArchiveProcessing_Day(); $archiveProcessing->setSite(new Piwik_Site($idSite)); $archiveProcessing->setPeriod(Piwik_Period::advancedFactory($period, $date)); $archiveProcessing->setSegment(new Piwik_Segment($segment, $idSite)); $archiveProcessing->init(); $notification = new Piwik_Event_Notification($archiveProcessing, '', array()); Piwik_YourPlugin::archiveDay($notification);