I think that some style of bulletproof coffee can be a worthwhile addition within your eating window, if you are following a ketogenic eating plan. It is important to have almost no carbs (usually under 20 grams ), as well as some protein, and the usual recommendation is 3-6 oz of meat.
The rest of your meal will be a large salad with greens and low carb veggies. In order to get the 70% fat in your diet, while still staying within the guidelines for protein and carbs, you will probably need to add some healthy oils.
Salad dressing made from balsamic vinegar and olive oil with a little himalayan sea salt will add some oil, and drinking a cup of coffee or tea that is blended with an oil, such as coconut oil, butter, or MCT oil, will also help keep your meal in balance.
Since I enjoy the taste of chocolate (and chocolates are definitely not on the program), I will sometimes add a bit of cacao butter to my bulletproof coffee , and this gives it that intense chocolate aroma and flavor.
What I use is made by Terrasoul, and is sold on Amazon, but there are other good brands available as well. Even adding just a little baking cocoa will add wonderful chocolate flavor to coffee, and adds very few calories or carbs, as long as it is pure baking cocoa.