To set your defaults go to General Setup > Default Auction Preferences and checkbox Silent, Live and Online. Enable pre-bidding under Silent and Live. Set the dates and times in all cases to the times and dates that you want to use for your pre-bidding auction. That way the online portion of the auction will cut off before your actual event and bidding continues at your event of paper bid sheets.
When you enter items, make sure to enter them as silent auction items with pre-bidding enabled.