If I suspect I have cataracts when should I call the doctor?

At your convenience. Not an emergency , but it is good to have an ophthalmologist examine and monitor your cataracts. Your quality of life can be vastly improved if they are treated when there is visual disability .
When vision blurry. Not all cataracts require surgery. If best vision is worse than 20/40 or glare is significantly affecting VA, most surgeons prefer to do surgery sooner but depends on pt's sx, risk factors, preferences; also, though no guarantees with any surgery, many patients are less dependent on or free of glasses after surgery; clear lens removal also possible in some pts; info: eyedoc2020.blogspot.com.
Cataract. In general, i will check a person's cataracts once a year to make sure they are not having a severe effect on the person's vision.
Eye exam. Typically cataracts are not an emergency. You should have them checked out when you think your vision has diminished.