As the others have said, as long as you are properly prepared, 14 hours should be doable. I've done it twice in the past year, both ways, and walking time has been around the 14 hour mark. The last time was in May, east to west, with Bill T, who as he said was suffering with a stomach upset. What Bill didn't mention was how strong mentally he is. I think it's probably 50% physical effort and 50% mental, you're going to feel some pain during any 40 mile venture, so you need to be mentally prepared for this. Bill, on the last occasion had a bit more to cope with.Lol.
Manandog said it was harder east to west, which is probably true, but I found it more enjoyable, i.e. you get the boring bits out of the way early (open moorland, bogs etc.) and have a nice challenge at the end. I love this this walk, it has a bit of everything, good for raising charity money too. Three or four of us are off again on the 29th July, east to west for a local childrens charity
Good luck with your walk, if you are properly prepared, shouldn't be a problem. Bit late to go in June this year though