If you do not have luggage and have a participating airline that you checked in at the hotel I would leave around 4. especially since they will drop you off at the departure floor....
I usually have flights about that time and we stay for the 3 pm parade hit the bathroom fill up the rental car and we are at the airport by 445. We have plenty of time to return the rental car, fanagle the car seat out, drag too much carryon stuff, a toddler and a stroller and make it through security with atleast 45 mins to spare which allows us to grab something to eat.
Now if we experience another airport security issue or threat level increases I might choose to leave a little earlier.