Probably awhile at that temp. Is the Traeger set at that temp or is that the verified pit temp? I usually cook chicken spatchcocked at 275 and it will still take me close to 2 hours for a ~ 5 pound bird
Ironwood 885, Char-Griller Flat Iron Premium griddle, InkBird Sous Vide
A whole chicken will take a lot longer than a spatchcock chicken, which will take longer than chicken parts. The more surface area that is exposed to heat, the faster it will cook.
Have your checked your grill with an independent thermometer to be sure the chamber temperature is what is shown on the controller? With most Traegers, there will be some error one way or the other. My Ironwood 885 runs at 200F if I set it to 225F. When set to 450F, it cooks at 400F. When you are trying to reach an internal temperature of 165F for chicken, a difference in cook temperature can extend the cook time significantly..
Always cook to internal temperature, never by cook time.