I would be too scared Ebay would turn the light switch off if I complained about something like that and asked for a bug fix. It would probably be the only time they ever fix a bug for me.
It is basing that delivery estimate (a guaranteed estimate if you are enrolled in GD) off of your history. If you ever got a similiar order to the hypothetical buyer zip code with the same type of postage carrier on the listing, it will make assumptions per your previous order history and track record. It may even consider the time of day, for example I believe the algorithm knows if I get an order at 8 AM, it will be shipped same day. It can tell whether you historically ship on time, early or late and will make a calculation. So if you have 3 business day handing but ship your orders same or next business day, your buyers will see a date based off same or next day shipping. Some call the 3 day breathing room, but if you aren't going to actually take 3 days, you are just possibly limiting your exposure in the search algorithm for points in the 'handling time specified in listing' variable. There obviously is another variable for 'handling time actually fulfilled by'
