<?php

    //primeiro sábado de fevereiro de 2018
    echo date('d-m-Y', strtotime('first saturday of february 2018'));
    echo "\n";
    //segundo sábado de fevereiro de 2018
    echo date('d-m-Y', strtotime('second saturday of february 2018'));
    echo "\n";
    //terceiro 
    echo date('d-m-Y', strtotime('third saturday of february 2018'));
    echo "\n";
    //quarto 
    echo date('d-m-Y', strtotime('fourth saturday of february 2018'));
    echo "\n";
 
    //quinto sábado - se não houver passa para o próximo mes 
    echo date('d-m-Y', strtotime('fifth saturday of february 2018'));