In his book On Writing, Stephen King says aspiring writers should spend four to six hours per day reading and writing. If he gave any specifics on how to divide those hours between reading and writing, I missed it.
Stephen J. Cannell said a writer should spend at least two hours per day writing, and even preempted a complaint from non-professional writers with a day job by saying, "make the time!"
During the week I set aside 10:45 AM to 12:45 PM for writing. On weekends I write when I find the time for as long as I can stand it before I pour the wine or head to a tavern. I read every night before bed and spend nearly all day on Saturday reading, and Saturday reading includes newspapers as well as novels. I also snatch books from my bookcases and read for a couple of minutes at random times throughout the day.
If you're an author with deadlines to meet, you would need to devote more time to writing than reading. You may still have to find time for other things such as another job to pay bills, laundry, and drinking. If you're not an author with deadlines, you can spend more time reading - but still don't forget drinking time.
From my own experience, I start getting shoulder pain after about two hours in front of a word processor.