It depends on your CCLL. The CCLL is your individual critical carbohydrate losing level. So if your CCLL is 50, you know that eating over 50 net carbs will knock you out of ketosis.
The CCLL is very individual. The Magic 20 for Induction was picked because that was the point when most people would be in ketosis. But for some folks, they start showing signs of ketosis when they drop their carbs below 100 grams daily.
I would caution about waiting to find your CCLL until closer to goal. See, the CCLL is an important number because it also helps you to find the CCML--Critical Carbohydrate Maintaince Level or the number of carbs you have to stay below in order to not gain weight.
Your CCLL can change. If you are exercising more and have more muscle mass than when you first found the CCLL, it can possibly increase.
Remember too, that ketosis just means that you are producing ketone bodies, which means you are breaking down fat. It doesn't tell you if that fat is from the fat you have eaten or the fat on your thighs. There's a transcript of an old Atkins Center chat online. In it the Atkins Center nutritionist related a story of a woman who wasn't losing weight but was in ketosis---she was eating a stick of butter every night for dessert.
Also when you overeat your carbs the ketones already in your body don't vanish they keep circulating in your blood and are in your tissues waiting to be moved out and used as energy elsewhere or burned in that cell for energy too. So many folks mistakenly see the ketones in thier urine after they cheat and say wow I ate ______ and it didn't knock me out of ketosis so I can have some of that again when in fact by Dr Atkins definition of ketosis as the burning of fats for fuel it did! After your body finished burning off the carbs you ingested and storing the ones it couldn't burn as fats and glycogen you then switched back to fat burning with more fat to lose. Remember every human being not hooked up to an IV feeding line is in ketosis every night while they are sleeping as the carbs and sugars injested during dinner are long gone and the body turns to those fats to keep you alive until breakfast time.
Yep finding your CCLL is i a very individual number and it is now called ACE on the Atkins site so when you see those folk with an ACE of 35 or 70 that is their number of net carbs for losing. Exercise vigorously can give you a huge boost in the number of net carbs your body can handle and still lose weight. Mine will change by over 65 net carbs if I'm working out or not going to the gym and just treadmilling.
Good luck with your journey x