Buses to Antalya from Fethiye are 365 days of the year, as is the bus between the otogar & Antalya airport. You'd need to allow IRO 5 hours in total for the journey, approx 4 to Antalya & a further hour to the airport, although if you got a taxi from the otogar journey time is approx 20mins only.
There's buses roughly hourly from early am to early evening from Fethiye