Well, look at the times Steve's comparing against. time() produces Unix timestamps - seconds since the epoch 1970 Jan 1 00:00:00.
In other words, he's comparing
1800 == 1970 Jan 1 01:30:00
2400 == 1970 Jan 1 01:40:00
1200 == 1970 Jan 1 01:20:00
And it's no wonder he's not seeing any difference.
instead of time(), use date('hi').
if (date('hi') > 1800){
Less expensive of course would be
$now=date('hi');
if($now>1800){
...