Reading notation is similar to reading english, there are some things that are difficult-some easier; there are some things I care not to read, and therefore shouldn't have to, and still others I enjoy to read even though they are very simple. My rule is five minutes or more almost everyday, as a warmup. I let myself do more, but never force myself; and if I am in a particularily bad mood perhaps none. I always bring myself back to the level I can read with least amount of strain and go from there, some nights I even just open a notation book and glance at the page and close it.