When you have to design a questionnaire, you have to ensure that you have a suitable question, and one that includes a realistic time frame.
In this case, you could use per day, per week, per month. Using something higer may give in accurate results.
You will also have to give options, these will be in hours or minutes, depending on the average amount of time.
You always have to include a 'None option', as some people may not read at all. For this, you could use 1-5 hours, 5.1- 10 hours, 10.1-15 hours, 15.1-20 hours, 20+ hours, none
In the average month, how much time do you spend reading?
0-5 Hours, 5.1-10 Hours, 10.1-15 Hours, 15.1-20 Hours 20+ Hours None