Nazir 56A

אוכל בקדשים לאחר ששים יום,

he eats sacrificial food after 60 days, when the status of uncertain tzara'at has passed, and when he has completed all his obligations of naziriteship. He cannot shave for his tzara'at right away, as he might be a pure nazirite, and the status of uncertain tzara'at does not override naziriteship. Instead, after 30 days he shaves for his uncertain status as a confirmed metzora and for his uncertain status as a pure nazirite. Once again, he is not permitted to shave a second time 7 days later for the shaving done by a metzora as part of his purification process in case he was not a metzora but impure. Were that the case, it would mean that the previous shaving was for his impurity, and therefore he would be required to observe naziriteship in purity for 30 days. At the conclusion of this period, i.e., the 60th day, he shaves and may eat sacrificial food on the following day, as even if he was a full-fledged metzora he has now shaved twice.

ושותה יין ומיטמא למתים לאחר מאה ועשרים יום.

And he drinks wine and may become impure to bury a corpse after 120 days. In other words, this individual has not yet completed his naziriteship vow, as he might have been a confirmed metzora, in which case both his acts of shaving would have counted for his tzara'at. He therefore waits another 30 days and proceeds to shave on day 90. Even at that stage, he may not yet drink wine or contract ritual impurity from a corpse, as he might have been impure, which would mean that his third shaving was for his impurity. Consequently, he counts another period of 30 days for his naziriteship of purity, at the end of which he may perform the shaving of purity, drink wine, and become impure from a corpse, 120 days from the start of his naziriteship.