When I didn't realize there was no sunlight left and I was still in there in the dark without turning on lights.
A friend who was over that day bought me a flexible flashlight to wear around my neck as a joke for Christmas.
Woke up from a sound sleep around 2 AM, and thought that since I was already awake, I could slip down to the garage, throw a few more coats of paint on the engine stand/rotisserie. And while down there, take measurements for the welding cutoff rack, maybe determine sizes of casters. Oh! And I need to move that bench to add a circuit behind it and..
When you're wrenching on the car with the garage door open and the sun goes down. And you keep wrenching and wrenching and then you hear the birds start singing like they do early in the morning before the sun comes up. And then the sun comes up.
I knew I was spending too much time in the garage when my wife developed separate knocks on the door to let me know when breakfast, lunch and dinner were ready.
I would have to actually drag my cold a$$ out there, shovel in front of the door, crank up the heat, go back later and start a job ....then......my wife might notice I am actually not in the house.
I just give myself a certain time when I'm going to quit for the night. It doesn't always work out to the minute, because I like to finish to a point, but it's close. I don't have to live in there, though maybe when it's finished, that might be more of a problem.