It also depends on the height of the
trees and your latitude. Can you get to this property to see for yourself? Luckily we're near the winter solstice now (close
enough) so the sun is as low in the sky as it's ever going to get right now. If you can get to the property and spend some time there, you
should be able to see how far back you need to clear trees from your site.
I'm guessing you'll be around 50 degrees North latitude. From a sun chart I'm looking at, for 48 degrees North the winter sun comes up at 8AM directly from the Southeast, hits 9 degrees off the horizon at 9:15, maxes out at 18 degrees at noon, drops back to 9 degrees at 2:45 and sets at 4 in the Southwest. Since you'll likely be a bit farther North, it's worse. To get 6 hours of sun there, you'd need to clear anything to the SE and SW that is higher than 8 degrees off of level. That is likely a long distance.
Good luck!