Everyone is different on this one. It can take some people a couple of days, some people longer.
Usually it takes me about 2 days however last week I had a cheat, woke up the next morning, no ketosis, and then by that afternoon I was in ketosis again. Didn't make sense because I know that cheat had WAY more carbs that I should have (Can you say Mexican food galore?) So that was a strange one for me! But nice!!

Just analyze what it is you are eating making sure that you are sticking to the right things. Also look for things that can cause stalls--artificial sweeteners, processed meats, etc.

Also remember that ketostix are not the absolute word on ketosis. You could be in ketosis and not show up on the sticks. Look for the signs--bad taste in mouth and others.

If you are sticking to your plan and still not in ketosis, Dr. Atkins touches on this in his book. I think he says to cut out salads. I don't remember.

GOOD LUCK!!