I’ve never been one to track ketosis, so I am not sure if it takes ages to get back in or not. As long as you keep the carbs down and don’t overdo the protein levels then I would have thought that ketosis would be unaffected even if calories are increased. Use one of the online calculators to work out approximately how much protein is required to maintain your health and musculature level (I did this ages ago and work on around 55-75g depending on my level of activity per day, I am not sure which calculator I used, but just used a search at the time). Try and have the same amount on 800 days and days off. You do get used to portion sizes so don’t have to weigh forever. If your protein is higher than the amount your body can use it could effectively act as additional carbs which may kick you out of ketosis. If you have set an 800 carb limit you may find you have to increase that to get sufficient vegetables and fruit on a ‘day off’, so I use 40g for 800 days and 60g to 70g for days off. This isn’t exact, rather it is an average, and if a day off does work out at lower than that no problem. Keep eating plenty of those healthy fats. Good luck! As always, your body is the important one so if anything makes it feel that you have tried something that hasn’t worked, just reset and try again.