I thnk we used to hack for about an hour - but this was years and years ago when we were on ponies and didn't have a trailer. We used to hack to shows as well. Of course there was less traffic about and the ponies were used to being ridden all weekend.
Years ago when we were kids I can remember hacking 8 miles to a meet/Pony Club Rally/show: and then doing the stuff, and hacking back again. It was a rarity to have one's own transport then, so you just had to.
I'll hack to a meet if I can do it in an hour at walk with the odd trot. But my hunter is a crazy fit, never tiring TB. Also only if the hunt goes in the general direction of home and not the opposite way.
I go about 45 minutes, but you do have to be careful not to end up miles in the opposite direction and to allow plenty of time to get home before the light goes!
I do about an hour, 6 or so miles (only go once a month or so, so he isn't super fit!- we don't do a full day though 11-3ish tends to work) though currently considering whether we can get over the level crossing. I do tend to check which way they are hunting though, and not go too far if they start heading the wrong way. Leave plenty of time to get home (always take fluorescents and have flashing LED leg bands in case) and the chance of an emergency lift if needed.
No more than a couple of miles. It's more me thinking about the end of the day and hacking home in the semi darkness potentially on roads after a day hunting - sometimes we are a long way from boxes too.
There are only a couple of meets I can hack too, and around 1/2 an hour away.
I remember my father hacking to meets and was the 'norm' in his day. He would regularly come home after dark luckily we lived down very quiet country lanes, but would not want to risk it nowadays.