Turkey hunting is typically done at that hour. I doubt she ever really hunted, but rather just checked out the dead animals with her bf. They did hunt in the woods surrounding the house. Clint wasn't always at the house so I am not 100% he knew her school schedule enough to know immediately that she had class and needed to leave at that exact minute to get there on time. I have lived with tons of family and friends and roommates and never known any of their schedules so precisely that I would immediately flip out if one of them deviated just a little.
I just don't find Clint's story as unbelievable as people think, or at least not for the reasons people cite. We have seen pictures of Holly and her Bf-they wore matching camo together. She helped him with animal corpses before and this is a hunting community. It just isn't unfathomable to me that he may think she was walking to the edge of the woods with her hunter boyfriend during hunting season and hunting hours. That is a reasonable conclusion to make as opposed to immediately thinking your sister is being abducted, in my opinion.
Now, the strange parts of the story for me are still centered around the timing, the scream, and possibly even the voices he claims he heard, yet didn't recognize, yet were "young."