It's a split depending on who you ask. Plenty of high scorers at my school saved it for the dedicated or after Dec...there are people that started using it at beginning of M2 as well.
I think it depends on how you learn. If you learn mainly from qbanks then I'd start doing them now and annotate. If you primarily learn from lectures and other resources, saving uWorld til at least Dec allows you to use it as an actual step 1 practice to identify weak areas.