How far is 2 to 2.5 hours driving for you, Mel?
For me 35 miles distance is about my limit but I don't time it. I would most certainly draw the line at 40 miles. I am guessing the longest time I would drive is a hour.
I reach most of my starting points via the A40/M40 which is a couple of miles from my home, and as I walk on weekdays I can't avoid the 15:30 to 19:00 evening peak when I return. It always means a half-mile queue along the inside lane of the A40 for my junction, and this is followed by a stop-start crawl for the remaining two miles. I just have to grin and bear it.
Edit: With such excellent walking country as the Chilterns AONB within reach as I've outlined above, I see little point in driving anywhere else. Mel's 2 to 2.5 hours would make Essex or Kent or the Surrey Hills, even the South Downs possible for me, but they would mean using the M25, ugh!
2nd Edit: I've since thought of another comparison. Two weeks ago I drove 100 miles and back on good roads (M25 and A12) which took 2.25 hours each way and used half a tankful of fuel in my little car. A fiddly, time-consuming bit was getting from home to the northern section of the M25, and back. At the end I was stressed and tired. Would I do that to go for a day walk? Absolutely definitely not!