Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Whistler to Mongolia as you normally would.
Vancouver Intl Airport is YVR and Ulaanbaatar Chinggis Khaan Airport is UBN. These codes are created by the International Air Transport Association (IATA) and airlines use them to identify the departing and arrival airports in the flight routes they service. Ulaanbaatar Buyant Ukhaa Airport (ULN), Dalanzadgad Airport (DLZ), Khovd Airport (HVD), Moron Airport (MXV), Ulaangom Airport (ULO) are other airports near this flight route and their unique identifiers/IATA codes.