When flying from Green Bay to Las Palmas de Gran Canaria, the time of day you decide to fly out makes little to no difference towards the overall price you’ll pay on tickets.
These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Green Bay Austin-Straubel Airport to Las Palmas de Gran Canaria Airport flight would often be abbreviated as a GRB to LPA flight.