"Doing keto" implies less than 20g/day on an ongoing basis, at least as I understand it. On top of that, one might have eaten early in the previous day, eaten no breakfast, and be working out about lunch time, which would provide the "at least half a day without carbs of any kind".

It may be that you disagree, but I get the feeling that you ignored the "doing keto" part of my setup, and instead thought that the person in question was eating cake 12.5 hours before the workout. :)

the specific number varies between different people. i'd say <20g is enough to get everybody into ketosis. <50g is enough for some.

It takes about a week of < 20g/carbs a day for the body to go into ketosis. This is born out by buying keto strips and testing your urine.

I can achieve 'dark purple' on strips in two to three days without drastic dietary or exercise extremes. This is one of my biggest sticking points with articles that make generalizations about body functions. There are always outlying examples and exceptions.

You probably already know this, but in case other readers don't, the depth of color on keto sticks is NOT a measure of "how deeply in ketosis" you are.

The depth of color indicates how concentrated ketones are in your urine, which is impacted by (1) the amount of ketones your body is producing, and, very importantly, (2) your hydration level (i.e. how diluted your urine is).

For newbies, if the stick is pink AT ALL, congrats, you're in ketosis. Don't make the depth of color a big goal.

this is not true for all people and urine tests are not considered reliable. I can get into ketosis in a single day of fasting

A little known fact is that you can induce ketosis while eating carbs. The biochemistry here is clear: You get into ketosis when you oversupply acetyl groups to the TCA cycle. Adding MCT (Medium Chain triglycerides) to your diet will do this.

I think this needs a little more explanation. Can you provide that?

Check this out: https://youtu.be/DG79PYeqZ78

It takes 3 days for me to hit ketosis at that carb level.