There was a thread about this not to long ago. You could do a search for more details.
Yes, there is a tour of Jiko & Boma. I believe the poster said that it was late afternoon - 3:45pm. There is a board in AKL lobby with these things posted on it.
This is not first hand knowledge on my part, I am going by memory of that thread, which I paid attention to as we are also staying at AKL in April & very interested in the tours.