It didn't take Sasuke a month to too get to Lee speed. It took Sasuke just a long to get that speed. The only differance was that Lee condition his body and charka to obtain his great speed, Sasuke on the other hand had been condition his body like Lee but not his charka, with the Sharingan Saskue was able to learn how to control his charka is a short amout of time to obtain that kind of speed. Reed the chapters when Lee and Sasuke first fought, In there it explains how Sasuke and Lee trained intensely like the other.