Why do you need to post more than once every 6 minutes?

The time limit goes down as soon as you enter your second activity period, by the way.

waittime = 360;
if(activity >= 15)
        waittime = (int)(90 - activity);
[other code removed due to irrelevance]

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Why would it be changed to, "the last posting from your account"? If anything, it would be IP/account.