If it's a specific case you're concerned about, why not contact Tim and ask him whether he would make an exception for you? He might not want that particularly advertised (or perhaps he might?), but until you ask him about it, you'll never know whether you could still return them or not!
I don't know for sure, but I would imagine the 14 days wouldn't include the postage time back to BKP. I think it means time to install, decide, then contact BKP if you're not completely happy - arranging delivery after that is a fairly trivial thing. Again I should stress, this is conjecture on my part. The best advice (as always) is to contact Tim directly :)
Roo