Just to clarify which = planetsim is referring to:
<?PHP
$hour = date("G")
if ($hour == "0" || $hour == "6" || $hour == "12" || $hour == "18"){
#do stuff
}
if ($hour == "1" || $hour == "7" || $hour == "13" || $hour == "19"){
#do stuff
}
if ($hour == "2" || $hour == "8" || $hour == "14" || $hour == "20"){
#do stuff
}
if ($hour == "3" || $hour == "9" || $hour == "15" || $hour == "21"){
#do stuff
}
if ($hour == "4" || $hour == "10" || $hour == "16" || $hour == "22"){
#do stuff
}
if ($hour == "5" || $hour == "11" || $hour == "17" || $hour == "23"){
#do stuff
}
?>
The first one is fine, where you are declaring your $hour variable.