In the strict definition of induction I did not last the two weeks because I could not do without my caffeine and cream.
In the wider sense of trying to keep around 20 carbs, that persisted into months and rarely got above 35. This was an OWL
period that lasted a year. During the year I experimented a lot with different carb levels, different foods and after a while you actually stop counting carbs as you eat them.
Low carbing for me became essential at the point of sale (ie in the supermarket reading labels)Working on the principle that if you do not have it in the house you can't eat it, and if its in the fridge or cupboard or vegetable rack then you can.
The interesting point to note is that there is no specific relationship to the amount of carbs you eat and either weight loss or weight gain. Everybody differs in their resistance to insulin.
Atkins set the limit at 20 to be sure he got in under the bar for most people. Other low carb writers and their plans follow the same basic principles but suggest carb levels of 40-60 which still achieve weight loss.
But in answer to the original question, there is nothing harmful in staying on induction for a long time, but it is restrictive, and is not necessary. Many return to a quick induction blitz to correct a few gained pounds on a maintenance plan.
That is where I am now, back down to near induction levels. This is because soon after the holiday period my scales starting playing up and telling lies (must get them fixed) and my clothes mysteriously shrank in the wash