Your question is in reply to these posts about cycling feast and famine cycles.
Their point is that it might not be best to stay ketosis always (low insulin always) - start at 2:20 on the “Feast Famine Cycles”.
What he seems to be saying is that the body will, after long periods of low insulin, decide a strategy of trying to defend body fat is good, so will start doing that.
Of course, this does not happen when fasting adaptations are happening because no food is coming in but, it could be a form of calorie restriction creating an adverse side effect.
So cycling out of ketosis and then back in seems to be the strategy he recommends (listen to the rest of the video for fuller details).
But, if your question is just how many carbs can you have - you can only tell that by going with the definition of being above 0.5 mM measured with a blood ketone meter. For a younger fit person, 100 grams of carbs followed by a HIIT workout and a 5 mile run will probably always keep them in ketosis (above 0.5 mM). But, a middle aged metabolically challenged person that is only either sitting in a car, sitting in a chair or lying in a bed my go below 0.5 mM with just 40 grams of carbs (especially if most were at a single meal).