There was talking going on in one of the CA/Browser Forum regarding certificate expirations, and how they looked at potentially 17 days. The 45 days was a compromise, but the whole 17 days was never removed from the table, and was still considered as a future option.
Honestly don't recall discussing 17 days, but I could be wrong.
47 days was a 'compromise' in that it's a step-down over a few years rather than a single big-bang event dropping from 397->90/47/less.
