This isn't really a PHP5 question, but anyway, here's an example
function isDateBetween($dt_start, $dt_check, $dt_end){
if(strtotime($dt_check) > strtotime($dt_start) && strtotime($dt_check) < strtotime($dt_end)) {
return true;
}
return false;
}
isDateBetween("2004-01-01", "2004-01-02", "2004-01-03")
and doStuffHooray();