Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from Tallahassee to London Gatwick Airport as you normally would.
Due to multiple factors, expect to potentially pay more when booking in December. For low rates, May can be a great choice for travel to London Gatwick Airport. Flights to London Gatwick Airport from Tallahassee in May are about $1,052 on average during May, but can be found for as low as $582.