The point of a ketogenic diet is primarily to lower your chronic insulin levels, though there are other benefits, as well. Lowering insulin is important for many reasons, one of which is that it is the primary hormone responsible for keeping us fat, since fatty acids are trapped in our fat tissue as long as our insulin level remains high.
If you are restricting your carbohydrate intake to ketogenic levels (we recommend an upper limit of 20 grams/day), then the glucose in your bloodstream is primarily the small amount that is produced naturally in your liver. There are cells in your body that do need glucose for their survival, but the liver is capable of making the small amount necessary. You could safely eat no carbohydrate at all, and be fine.
If your schedule does not permit you to eat early enough to have a foodless period of several hours before going to sleep, then so be it. Don’t worry about it unless you are not seeing the results you want. The human body is designed to cope with fluctuations in insulin—after all, we cannot stay alive without a certain minimal amount in our blood. The problem comes with chronically elevated insulin levels (hyperinsulinaemia) which, like chronically elevated glucose levels (hyperglycaemia), cause damage to the body over time. Hence the carbohydrate restriction—carbohydrates are nothing more than long chains of glucose molecules, and glucose is what stimulates insulin production the most. Protein and fat have a much lower effect, especially in the absence of carbohydrate in the diet.