Re: 5:15 The Angels Have Gone.
It reads very well and I didn't have any trouble following the narration or the action. As to leaving the ending ambiguous, it depends on what you mean by that. I don't think you're giving anything away, unless you're implying this guy only has seven days to live. However, the driver of the lorry will probably call this accident in. The odds of your character being trapped in the car for seven days aren't that great.
On reflection, though, I don't think you need the horse. A road like this is foggy and icey enough to cause an accident on it's own. And one picky thing, on this line
...thin, handsome, and popular, not the fat mess he was in reality this way.
I'd cut "this way" at the end of it. I think it would read better without it.
Good luck with your story.