Hi Chelley. It's really hard to talk specifics as we're all so different. I asked my BS how long he thought my tumour had been growing and he thought that maybe two years, but that the DCIS could have been there for fifteen.
Your docs would have looked at the pathology of your DCIS and have a pretty accurate idea of how it's behaving. There are lots of markers that are examined. I would try not to worry about the time at this stage.
I think that having a sentinal node biopsy is a cautious, excellent idea. Knowing if you've got any spread to your lymph nodes will change and refine your treatment. Simply put, it's going to give you and your doctors more knowledge about your cancer and that's a good thing.
Multi-disciplinary meetings are the gold standard of cancer care. It sounds to me like you're in good hands. Hang in there. K xox