When I was racing frequently (back in the 20th Century) I typically did 4 runs per week, totalling 3-4 hours, including one speedwork session. Whenever I tried doing more than that, I got injured; but in any case I was able to race at a level that satisfied me.

A few years ago, when I got the strange notion that I would like to do a few races again, I started doing 3 runs per week, totalling 2-2.5 hours (having been running once or twice a week in the intervening period). But see my recent post on the Injuries forum: last week I did two runs, totalling 1hr45mins, and I am still trying to recover from that!