Because my schedule can vary from day to day, my eating window is from 11am-3pm. That way, regardless of what time I get home from the fitness center, I can make my meal sometime in that 4 hour time frame.
However, this does not mean that I can eat for the whole 4 hours, I just have the one meal, and probably spend less than a half hour when I am eating that meal; so I am actually fasting for 23 hours and having one meal per day.
That is one of the things that I really like about OMAD, is that you can have a flexible eating window, so that sometime during that 4 hours, you know you will be eating, but it does not have to be at the exact same time each day.