Being early for session is impolite.
When a client arrives early to the dungeon, there is often nowhere to put him. Most dungeons do not have waiting rooms due to matters of privacy and space. I do not enjoy shuffling clients around the establishment, which is what happens. It takes up my prep time and interrupts the flow. Occasionally, all play rooms are in use, so the early bird has to wait in the bathroom, meaning the facility is unavailable for Mistresses and slaves that may need its use.
Sensitive to mood, I enjoy a relaxing transition from the time I leave my apartment to the time we meet. I walk to midtown listening to music, blood pumping from physical exercise and emotions stimulated by the tones and lyrics of song. Once I arrive at the play space, I take time to set up the room, making sure everything is in place, the lighting is right, and the equipment selected. After the environment is ready I change into my fetish clothing, completing my preparation and feeling the fantasy.
If the client arrives while I'm getting dressed I'm not going to answer the door. Unlaced corsets and half nudity are not part of my opening act.
If you are early for your appointed session, I suggest biding your time in the neighborhood. Near the Parthenon there's a lovely Japanese coffeehouse, a massive beer bar, and various little shops and cafés. If you need to use the restroom before session, most of these places can accommodate. The best idea, of course, would be to run an errand for your Mistress. I always appreciate a bottle of water or a hot green tea. Do not wait outside the entrance of our building - respect others' privacy.
Arriving a couple of minutes early is not a big deal. Come on up. Arriving any earlier will impede upon the preparation I need to craft our time together. Respect that.