Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Yogyakarta to Nanjing as you normally would.
This is defined as Yogyakarta Adisutjipto Airport (JOG) and Nanjing Lukou Intl Airport (NKG). Codes like Nanjing Lukou Intl Airport are often used to just call airports uniquely.