Not certain of the answer. Anecdotally, over the years people taking vitamin C and lysine drink mixes at therapeutic dosages reported "best results" taking about 20 minutes prior to meals. (Less gas and discomfort I presume.)
As Hickey/Roberts report in THE RIDICULOUS DIETARY ALLOWANCE (lulu.com/ascorbate) some amount of ascorbic acid is absorbed through the stomach wall, so almost instantly.
For that AA that reaches the gut, between 1/2 (Pauling) and 4/5 (Catchart) is lost, i.e., degrades or is not absorbed so is not bioavailable. (Since some is absorbed into the blood stream through the stomach lining, the lost in the gut may even be greater.) It seems that for this portion of the oral vitamin C intake, traveling into the gut, then yes, taking with protein (and avoiding carbs) would seem prudent.
Another variable to keep in mind is transit time in the stomach. According to Dr Levy in one of his books (Optimal Nutrition) carbohydrates stay approximately 2 hours in the stomach, proteins last four hours, and fats stay in the stomach approximately 6 hours. From this one might conclude that the optimal time to take vitamin C is 2 to 4 hours after a meal, after the carbs have passed out of the stomach.
Owen R. Fonorow, Orthomolecular Naturopath