Re: How long did you leave it before you hacked out your new horse?
We just got a new horse too, and the owner insisted on bringing him to our yard, instead of us going to see him when we wanted to try him out. He had mostly been a 'back up' horse, and had been taken out of the field on random occasions for the odd pleasure ride / hack, so was used to going to random places. He arrived, was tacked up on our yard, and I rode him out around the farm. The owner then left him with us on loan the same day, so the next day I took him out again, and we went on from there. He settled in immediately, and we have never had a horse that has made himself so at home so fast! He is still a little nervous of random things (happily walked past a hedge cutter in action, but freaked at a log in an open field!) but that may just be his thoroughbrediness! Basically, what I'm trying to say is it's each horse to its own, but the sooner you can get them established in a routine the better, and it's often better to start of with short hacks near home first. Even so, if I had a choice I would definitely do want Sonia suggested with any other horse, instead of jumping straight in the deep end like we did with Beau!
Good luck! Hope it all turns out well for you and your new horse! Xx