You don’t need to fast longer between the two meals, your already fasting for 17 hours out of 24, fat burning will be happening during those 17hrs. To be honest you don’t need to fast to be burning fat, I don’t fast I eat 3 times a day at roughly 7 am, 12.30pm and 6.30pm and I’m in ketosis and fat burning.
I really think you are overthinking this and are doing fine on the regime you are on