When I was detailing professionally, I often neglected my own vehicle as well. It was silver so it tended to hide a lot, but I definitely let it slip. It would be embarrassing when a customer would ask, "Is that your car?". Then you start with the excuses. I was always so focused on booking someone else, that when I had free time to do my own car, I never wanted to.
My best recommendation looking back on things, is once or twice a year properly prep your car. From there on out I'd schedule your own car for a quick maintenance every 2 weeks or so. As long as you consistently maintain your vehicle properly, it shouldn't take much more than 1.5 hrs for a quick wash & wax, dress tires, and a quick vacuum and wipe down of your interior. It only becomes time consuming when we let it slip, and that's when you don't want to do it the most because you know that it's more work. Schedule yourself like a customer and try to stick to it. You may gain a customer by having your car looking clean all the time. I've had people talk to me at the gas station, in parking lots, rest stops, etc. and some turned into customers. At the same time, you don't know if you're giving a bad impression to your current customers if you neglect your own vehicle. If you do neglect your own car, I hope you have an amazing rep to back it up.
George