I did full on Keto prior to a diabetic diagnosis, purely to lose weight. I lost 25 Kg in 4 months ( a sack of spuds ). I have no idea what my blood sugars were at the time, as, as far i was aware i was not a diabetic. although since i had peripheral neuropathy symptoms for 3 years prior to this, i think now i must have been. Shortly after that i was diagnosed as pre diabetic, and now believe the result was skewed, due to the strict Keto i had done. Nowadays i do low carb, i don't measure the carbs i eat, but do avoid as much as possible. My sugar levels tell me if i'm eating a low enough amount. i am convinced if i did strict Keto again, my levels would be in the 4 - 5 range, but i'm happy with them slightly higher, keeping full on Keto in my armory should i require it later. However we ARE all different, and the results i see may not be what you would, maybe not as good as yours.
Intermittent fasting is believed to start fat burning in as little as 12 hours once you are fat adapted. The reason the first time into Ketosis takes some effort and time, is the fact as a species we have forgotten how to utilise this amazing adaptation. Once relearned the body can switch quite quickly between glucose and Ketone bodies as fuel.