Thank you for your enquiry.
The bad news is that in fact the advance Reminder option is only available with GroupWise 6.5.2 and later. (The GroupWise feature on which Anniversaries depends, Delayed Delivery, was introduced in GroupWise 6.5, but was defective until the release of 6.5.2.)
I am sorry about the misleading documentation, which has been updated in the current release. You should be able to download and install Anniversaries 2.0.6, which is a free upgrade to Anniversaries 2.0.x. Alternatively, if you have installed Calendar Pack 2.0 (which includes Anniversaries), then you should download and install the current release, also available here .