Can I return the car at 4am due to flight leaving early?

I have returned cars early

No! You cannot! It's the only bad thing I can say. They do not open until 5a. The gates are closed and there is no option but to wait.

Call them just in case. Each branch has different hours of operation.

I do not know. I would call the number to confirm. I would think you could. It was super busy also. So going early is probably a good idea. Good luck.