You're assuming that Regulation DD is your only concern when you are imposing a charge on IRA participants?
The penalty you are considering isn't on the time deposits the IRA holds, it's on the action the participant is taking; i.e. he's not just taking the funds out, he's taking them to another bank. You need to get some advice from an attorney who can tell you what the acronym "ERISA" stands for before you begin the conversation.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.