The United search engine is offering you the June 16 12:28 a.m. departure and is also offering you the June 17 12:28 a.m. departure.

For flights departing about 0000-0200, a search on either that flight's day or the prior day will return the flight.

This happens because if you wanted to fly "on Friday night" you might also be willing to fly Saturday just after midnight. But you might ALSO know that there is a Friday 12:28am flight and quite reasonably have said "this leaves on Friday, please show me!".

The United UI tries to tell you this by explicitly mentioning the date of the 6/17 departure and saying "please note this flight involves a date change". I agree it's still pretty subtle.