Zeroes your first month

[Pootz]

I took 6 zeros the first month. 1 injured, 1 sick, 4 weather.

[Grampie]

I would think that it depends on a lot of things. What kind of shape you are in, how old you are and what kind of weather you are having.
If you are not in the sub 40 group and in good shape you should think about taking a "0" every 5-7 days just to rest up a bit. After you are in "trail shape" you will be fine not taking any unless you have to.
Listen to your body. It will tell you when you need to take a "0" day.