<select name="saat">
<?php
for ($saat = 1; $saat <= 23; $saat++) {
    $baslangic = str_pad($saat, 2, "0", STR_PAD_LEFT) . ":00";
    $bitis = str_pad($saat + 1, 2, "0", STR_PAD_LEFT) . ":00";
    echo "<option value=\"$baslangic - $bitis\">$baslangic - $bitis</option>";
}
?>
</select>