M:B:T time 1:01:000 is locked to SMTPE 00:00:00:00 in Cakewalk, and cannot be changed.  If the song starts with a partial measure of "pick-up" notes, then the first downbeat will have to start on 2:01:000.  For this and other reasons, I do not find automatic tempo detection to be very useful.  I've posted versions if the following manual procedure using Set measure/Beat At Now (Shift+M) many times, and still find it give the most predictable and precise results. Easier to do than to describe: