I wonder if your face is slightly swollen in the morning, and then it subsides after a couple of hours. I had no idea what would cause that, so I googled it. One reason could be allergies. Do you think that could be it? I recently saw a tip that people with allergies to airborne allergens should change their pillowcase every day, because the allergens get into hair and thus the pillowcase. Might be worth a try if you think allergies could be the problem.
Back when my facial hair was still jet black, I used to shave with an electric Norelco, and would always have a “shadow” by mid afternoon. I finally switched to shaving with a blade, and that kept me looking trim well into the evening.
Now that I’m more salt than pepper, I can go days without any obvious stubble! Yay, old age!
Thank you for your interest in solving this minor mystery. I don’t think that’s it because my face neither looks nor feels slightly swollen in the morning. And as far as I know I have no current allergies.