I found a solution
add_filter( 'bp_activity_permalink', 'bpdev_custom_rtemove_perlink_from_timesince',10,2 );
function bpdev_custom_rtemove_perlink_from_timesince( $time_since, $activity ){
$action = $activity->action ;
$time_since = '<span class="time-since">' . bp_core_time_since( $activity->date_recorded ) . '</span>';
$content = sprintf( '%1$s %2$s', $action, $time_since );
return $content;
}