Proper cyclists target hours not miles. You can't compare miles in say flat Essex with hilly Cornwall or miles on a 26lb nobby tyred bike to a 13lb bike with latex tubes and race tyres.
Your target should be what you feel you need or desire, not dictated by somebody else. That said I'd have thought you might want to do at least 4 hours a week for fitness/weight loss, maybe 8-10 if you're a keen cyclist and 20+ if you're very serious or a pro!