I've always found that the first time I do any particular journey whether it's on foot, by bike or in a car then it seems to take forever. Subsequent trips feel much quicker, even if they probably aren't, as I tick off features or points of interest or whatever as I have subconsciously split the route into smaller segments.
My point about LDWA members on the BGR wasn't that they could just turn up and do it but that with a bit of training or route adaptation, i.e. getting some climbs done, then they'd be as likely to succeed as a fell runner whose longest race or runs were in the order of a typical medium length race.