Is there a minimum time required between items in a group to assure subsequent bids won't execute in the event an item is won?

Sellers seem to be now scheduling multiple auctions very tight to thwart group bidding so I'd like to set the time very tight--but don't want to accidentally win multiple quantities of the same item.

Yes, there is a minimum requirement for this.
Please check the following FAQ section for more information on that:
http://www.myibidder.com/login/faq/2/#q12