What was said above.

I actually happen to like that it does this, because when I want a red eye, I don't need to search twice depending on what leaves just before and after midnight. As an example, I always have to connect from west coast (- CVG). The SFO-ORD departures, for example, mostly leave before midnight, but sometimes, there is one that leaves a bit after, and any SFO-IAH connections are usually post-midnight. So in this case, I only need to search once, and it brings up the options with both, say, late Sunday night and early Monday morning departures.

You do have to take note of the date at the top, especially when it is offering both pre- and post-midnight departures. Because, for example, if I specify July 1, both pre-midnight departures on 7/1, and post-midnight departures (early 7/2) will note a date change - in the first case, since you are arriving a day later, and the second, since you are actually departing on a different date.

Never thought much about that actually, but maybe a good piece of feedback to differentiate these message (besides the +1 on the arrival time), for example, pre-midnight departures could state in that yellow something like: "Please note the departure date is 7/1/2016, and arrival date is 7/2/2016", while post-midnight departures could have the box in red, and note "Please note the departure is early morning on 7/2/2016".

I think the reference was to the fact that SEA-ORD is going to literally be the same mileage/distance one night vs. the next.

On the other hand, based on specific circumstances each day, the actual flown mileage will be different...based on winds and how you might have to depart origin and approach destination differently, how you route based on weather patterns each day, etc.