The function lets you search for the route with the latest departure time that will allow you to reach your destination on the day concerning which the date and time search has been performed*.
Also, if the arrival time at the destination is the same, routes with the later departure times will be given priority.
*Definition of the “day concerning which the date and time search has been performed”
The “day” is specified as the period spanning from 3:00 a.m. to 2:59 a.m. of the following morning.