The F lounge is certainly open 24 hours, the nighttime is the busiest for the airport, it is comfortable, with a full bar and buffet as well as excellent showers

One thing though. I remember the opening of check in for flights was not until 4 hours before departure (check with EK) about their policy regarding this as things may have changed, so careful about leaving the airport as I got stuck going KUL-DXB-EWR on MH couple years ago because I went into the city