7 miles from home, takes no longer than 15 minutes, and 20 minutes from work. Not ideal but nicest yard. I have lots of yards very near me but they have very restricted turnout and I wouldn't want that for my horse.
6 miles from home, but under 3 from work. It can take 40 minutes to get home if something's happened on the M1 or M25, it all merrily backs up to our back roads.
Not a yard but fields...2 mins down the road in the car or a ten minute walk
Wouldn't want to travel more than a few miles due to my personal circumstances x
My first yard (for 4 years) was 20mins away from home, but on the way to work. It was assisted so I only went once during the week, and had lots of helpful people and an on-site owner who was always happy to chuck in a pre-prepared haynet etc if they were in during bad weather. After I had my daughter though I changed to one that was in walking distance and about 4mins by car, which made a huge difference even though it was full DIY. I don't think I could set a maximum, as it depends so much on the yard and your lifestyle at the time.
I now have them at home! (sorry, new so not quite sunk in yet).