How long does it take to go keto? It depends entirely upon your confidence and what you want to do. There are some people with Type1 diabetes who seem to be able to achieve good control and at the same time eat a low fat high carbohydrate diet. They do not seem to get complications with slightly higher Hba1c. Such people are probably happy the way they are and will not be looking to change things.
Then there are others who are keen to start soon as possible because they feel that their control is poor. It is up to the partnership between you and your clinician to work out how quickly the transition to a low carbohydrate or ketogenic diet should happen.
It is probably not helpful to emphasise nutritional ketosis in type 1 diabetes. Achieving nutritional ketosis can become an aim in itself. It is not the prime aim. That is to achieve long periods of normal or near normal blood glucose. We are emphasising the need to reduce carbohydrate intake so that the body primarily utilises fat for energy. So, because the result of fat burning is ketones, the diet will be ketogenic. However, Type 1 control will at some point require glucose supplements to ensure safe management of hypos, and sometimes the basal insulin dose might be less than ideal in times of stress and infection. The effect of stress hormones in raising blood glucose might throw you out of ketosis. It doesn’t matter. If you manage the basal insulin levels to the optimum and are confident in carbohydrate counting you should be able to achieve good blood glucose control and get to adequate nutritional ketosis within 2-3 weeks of starting a ketogenic diet. But equally it is perfectly ok to go more slowly and reduce the carbohydrate in one meal at a time in a stepwise fashion over several weeks. You might for a start prefer to low carb just one meal at a time. It is individual. This is a lifestyle that you base around your requirements. Many people might not want to go to very low carbohydrate diets in the 30g a day range but prefer to use more carbohydrate.
The aim is to simply achieve near normal blood glucose 24 hours a day. It is not unrealistic to expect this with a lowered carbohydrate approach to dietary management.