I am not going to try to figure out what date/how long she has been locked up, because I think that's her private life and it feels a bit invading to her privacy. But, I did think I figured it out how it works with the release/locked up thanks to having the book, so I will try to tell everyone in a way one knows it but the book doesn't get spoiled. I try my best to keep spoilers out.
Miss Autumn have had, as mentioned before on this topic, several experiences with both mental health care, 'shrinks' and suicide before she eventually got locked up (sorry I don't know a more subtle way to put it, my English is pretty bad). When you listen closely to Opheliac, you will also notice none of the songs are actually about being locked up, rather about mental illness and medication in general. Due to a series of unfortunate events, Miss Autumn tried to drown herself in a lake. This is was when she made the deal with herself about finishing Opheliac. Thus, she started working on Opheliac, but then something bad happened which I won't mention because of spoilers, and if I am correct then she took all her sleeping pills and got locked away. This would make sense as fLee said it was in 2006 and Opheliac as well as the European tour were later in 2006/2007. Thus she was almost finished with Opheliac when she got locked away, as she mentioned she was already done /writing/ Opheliac, but not editing/releasing. Eventually when she got out she finished Opheliac (probably editing) and probably felt like she had a purpose and thus kept her promise to herself
I hope this makes sense and please realise this is just what I figured out, not the absolute truth ( I could be so off that the people who know her laugh so hard the tea drips out off their cups). I tried my best to explain without invading too much of her privacy.