Ondertussen is het gelukt;
Misschien niet de makkelijkste manier, maar het werkt voor mij!
$date = time();
$day = date('d', $date); // Dag
$weekday = date('w', $date); // Dag van de Week
$week = date('W', $date); // Week nummer
$month = date('m', $date); // Maand nummer
$year = date('Y', $date); // Jaar
$first_day = date("w", mktime(0, 0, 0, $month, 1, $year)); // Eerste dag van de maand
$total_days = date("t", mktime(0, 0, 0, $month, 1, $year)); // Aantal dagen van de maand
$get_year = mktime(0, 0, 0, 1, 1, $year);
$get_month = mktime(0, 0, 0, date('n', $get_year), date('j', $get_year)-(date('w', $get_year)-1), $year);
$get_week = mktime(0, 0, 0, date('n', $get_month), date('j', $get_month) - 7*(date('W', $get_month)-1), $year);
$monday = date('d-m-Y',mktime(0, 0, 0, date('n', $get_week), date('j', $get_week) + 7*($week-1) + 0, date('Y', $get_week)));
$tuesday = date('d-m-Y',mktime(0, 0, 0, date('n', $get_week), date('j', $get_week) + 7*($week-1) + 1, date('Y', $get_week)));
$wednesday = date('d-m-Y',mktime(0, 0, 0, date('n', $get_week), date('j', $get_week) + 7*($week-1) + 2, date('Y', $get_week)));
$thursday = date('d-m-Y',mktime(0, 0, 0, date('n', $get_week), date('j', $get_week) + 7*($week-1) + 3, date('Y', $get_week)));
$friday = date('d-m-Y',mktime(0, 0, 0, date('n', $get_week), date('j', $get_week) + 7*($week-1) + 4, date('Y', $get_week)));
$saturday = date('d-m-Y',mktime(0, 0, 0, date('n', $get_week), date('j', $get_week) + 7*($week-1) + 5, date('Y', $get_week)));
$sunday = date('d-m-Y',mktime(0, 0, 0, date('n', $get_week), date('j', $get_week) + 7*($week-1) + 6, date('Y', $get_week)));