Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Qatar to Guam as you normally would.
Related info for your journey
Useful info, stats and facts about Qatar to Guam flights.
These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Doha Hamad Intl Airport to Tamuning Guam Intl Airport flight would often be abbreviated as a DOH to GUM flight.