Problem solved re-invent the wheel. add to functions to the include
file

function Sunday()
{
$day = 86400;
$stamp = time();
$sunday = date('w',$stamp);
$stamp -= $day * $sunday;
echo date('Y-m-d',$stamp);
}

function Saturday()
{
$day = 86400;
$stamp = time();
$sunday = date('w',$stamp);
$sunday = 6 - $sunday;
$stamp += $day * $sunday;
echo date('Y-m-d',$stamp);
}