I don't believe you would get all the benefits. Some people do a "one meal a day" kind of keto diet, where they just eat one big meal each day and fast the rest of the day. Without keeping your carbs down all day you wouldn't actually end up in ketosis. If it seems too daunting (I know it was for me at first) you could look into "dirty keto", "lazy keto", or "dirty lazy keto." I follow dirty lazy keto - I don't count macros except for carbs, I keep them within 50 net carbs per day. I eat meat and cook with oil or butter, so my fats are probably within the ranges they need to be. It's been working for me. I mostly eat a lot of vegetables and meats, with a little butter / olive oil thrown in. It takes a while to get used to, but there are recipes to replace a lot of the carb-laden foods, such as keto breads, etc. You really don't have to buy a lot of expensive stuff either. I think if you're going to do keto, of some sort, you should be consistent to get the benefits, or your later meals will just cancel out the benefits of your keto breakfast.