I'm kind of in the middle of answering your question so I don't have a definitive answer but can offer some info.
I started a few slips of regular orange sweet potato 8-16 as part of an experiment on using Hügelkultur in containers. They took off almost immediately and offer promising results. My first frost is usually early Nov. and will kill these vines. At that time, I can have somewhat of an answer to your question. This would be about 70 days to maturity vs normal time to maturity of about 120 days.