Okay, of the original batch of 7 hatchling tadpoles I had, back legs had emerged on most by June 9th. By the 17th, three of them had front legs and all had morphed by the 5th of July. That's about 8 days at the soonest. However, they'd been kept in a very small tank for most of that time, which made it more difficult to control the water temperature and quality. It often approached 80 degrees F, which made me move it around the house until I was able to find a cooler spot until I was able to move them to a larger tank (Yes, I was ill prepared in my spontaneous decision to raise tadpoles, and this forum was a godsend)
The second batch of 23 were caught from a later hatching, kept in a bigger tank, and developed a little more slowly. Temp was still in the low 70s though.