Checking out a day or two early has never been a problem. I let the front desk know the day before usually, or whenever I know I'm going to leave. I've never been charged a night or a fee in over 20 years. If you plan on staying in the room past 4:00 PM (or whatever checkout time you have) then you will have to pay either a day rate or the rate for the night, but for evening flights, just hang out in the lobby or lounge until it's time to go.