The objective is same-day arrival, and it works pretty reliably as long as you order by 3pm or so (in my area, at least). More importantly, you're given a clear indication when you order when you will actually get it (you can choose a delivery window, and see which ones are greyed out).
The delivery windows go as late as 9pm, so I'm sure they will try to push back the last time at which you can order and still get it delivered same-day.
The delivery windows go as late as 9pm, so I'm sure they will try to push back the last time at which you can order and still get it delivered same-day.