When you are creating your auction, you will have an option for one or multiple time blocks. Add the name of the time block and select a new start & end time. When you edit a time block, it will update the date and time for every items already assigned to that time block.
1) Click "Auctions" on the far left.
2) Click on "Manage Auctions".
3) Click on the Name of your auction.
4) Click "EDIT".
6) Add new time blocks or edit existing time blocks.