Basically, immediately. I always ask people to start with breakfast. Try low carb pancakes JUST ONCE and you’ll see how much better your blood sugars are THAT very day. It takes a few weeks to a few months to master dosing for protein and adjusting basal rates down, as most people need to do once they go low carb. It takes time to observe how different meals affect your blood sugars. I would highly suggest buying a blood sugar journal so you can document your outcomes and recognize patterns.