Get the First Saturday of the Year

function get_first_day($year = false, $month = false, $day_number = 1)
{
  $month  = ($month === false) ? strftime("%m"): $month;
  $year   = ($year === false) ? strftime("%Y"): $year;

  $first_day = 1 + ((7+$day_number - strftime("%w", @mktime(0,0,0,$month, 1, $year)))%7);

  return @mktime(0,0,0,$month, $first_day, $year);
}

Content: Day numbers refer to the matching calendar days.