All timestamps returned by FlightXML2 are in epoch seconds in UTC/GMT timezone. You will need to convert times to local timezone if that is what your application requires. The AirportInfo function will return the POSIX timezone identifier, which you can use to convert epoch seconds to another format.
FlightInfoEx does not permit you to filter flights by time range. The expectation is that you pass a large enough howMany argument and then your application looks at all of the returned flights to find the one or more flights that are of interest.