I personally had to do my diet for 3months before I was told I could start trying for a baby. The levels went down VERY quickly, but they just wanted to make sure that my levels were stable before starting to try. I hadn't been following the diet AT all before I decided to go on the preconception diet, and the levels went right down as soon as I started doing the diet. It is always better to plan for these things yes. However MY dietician said that as long as the levels are down within the first 10 weeks, everything SHOULD be ok.
I would advise to add Louise84 (I think that is her name). She had 2 unplanned preganancies, and she has been through it. She is always willing to talk and to help other people! Im sure she will reply on here when she sees that you need help!
I can only tell you to read my blog, I planned for my pregnancy but I have had high levels on and off. I can only tell you what I know. I know Louise will help you though.
Please keep us updated with how everything goes! I wish you and your partner all the best x x