Femara cycle days??

Jennifer • Due date 10/3/2016 with my 🌈👶🏼. DD 4/13/99 💞. Angel baby 👼 5/22/2014.
Does anyone know why some docs perscribe Femara different cycle days?!?!  My doc prescribed mine days 5-9 & I've seen where most do cycle days 3-7.  Do u know the why the difference or does it even matter??