I'm not sure if the following is only for Prime Members or not, but I have noticed that Amazon will sometimes ship multiple items from the same order on different days or by different carriers. Even if you add an item or two to reach the $35 minimum for a 1-day or same day delivery, the added items might not be in stock at you local warehouse and thus will probably ship in their normal time frame. For example, one item is listed as same day delivery, but a second item is listed as 2-day delivery. So in other words, Amazon will go ahead and honor the same day item delivery rather than wait and ship it with the 2-day item. Just because we place multiple items in a single order doesn't mean they will ship the same day, by the same carrier, come from the same warehouse, etc. It is better for Amazon to combine items into a single box, but they cannot always do that.