If I understand your problem correctly, you just want to display one of a number of messages based on the current time, then quit.
UPDATE: As noted by Ikegami below, this is wrong!
"So take the current time in seconds; mod it by the total number of seconds in a message cycle, and divide the results by the number of messages you have:"
The correct formula (Thanks to Ikegami again) is (time / message-display-time) mod number-of-messages.
# See correct version of this by ikegami below!
@message = ("Message 1",
"Message 2",
"Message 3",
"Message 4",
"Message 5",
"Message 6",
"Message 7",
"Message 8",
"Message 9",
"Message 10");
$num_msgs = @message;
$msg_time = 5;
$total_time = $num_msgs * $msg_time;
$msg_num = int((time() % $total_time) / $num_msgs);
print $message[$msg_num], "\n";