It seems that not all flights are being returned by the API after a certain time of day. For instance, when I query this endpoint flightxml.flightaware.com/soap/FlightXML2/wsdl with the same airport codes and different times, as soon as I pass in a time that is after 3:59PM PST, the API only returns flights for the following day despite there being valid flights after that time the same day. We are using a 24 hour window.
Passing in 1452643140 (3:59PM PST) returns flights after then and before midnight as well as flights for the next day.
Passing in 1452643200 (4:00PM PST) only returns flights for the following day.
My guess is that since 4:00PM PST is midnight UTC, this may be causing the behavior. However, if I convert PST to UTC, that will not return the same day flights.