It appears that there is a bug in Outlook 2010 related to delayed delivery of an appointment email. We are using Lync 2010 as well. You can test this by doing the following. Create an appointment in Outlook by clicking "New Online Meeting", add a few attendees, select the File tab, click the Properties button within the Info section, within "Delivery Options" select "Do not delivery before" and set a future date/time for delivery. When you send the appointment it goes out immediately and is not delayed.
FYI, I noticed that I can't do delayed delivery of a non-Lync online appointment. Maybe this is an issue when the Lync plug-in is working with Outlook.
Can someone confirm if this is a bug or a configuration issue on our end?
Thanks