$min = some number if defined
$max = some number if defined
$Files = some number 
$IdleTime = some number 

if (defined($max)) {
    $if = "($Files >= $max)";
}
if (defined($min)) {
    if ($if) {
        $if .= " || ($IdleTime >= $min)";
    } else {
        $if .= "($IdleTime >= $min)";
    }
}