As far as I know, commuter railroads have been counting the post-midnight departure from the city terminal as the last departure of the previous day, rather than the first of that day, because riders use that train that way.
Ditto a corridor train like the last Lincoln Service into St. Louis or the last Wolverine into Pontiac, both leaving Chicago in the afternoon/evening and arriving at the terminal station after midnight.
I think most people consider a departure at a decent hour arriving at the destination in the midnight or even 1am hour to be less-than-ideal but still essentially a same-day trip.
Ditto a corridor train like the last Lincoln Service into St. Louis or the last Wolverine into Pontiac, both leaving Chicago in the afternoon/evening and arriving at the terminal station after midnight.
I think most people consider a departure at a decent hour arriving at the destination in the midnight or even 1am hour to be less-than-ideal but still essentially a same-day trip.