Billy's leg 1 time is a bit too quick, I've been told by those that know better than me. He set out fast and suffered for it later on - at Honister a 'Naylor Shake' was required to sort him out!
One of the reasons people may have been put off fast attempts is looking at this Leg 1 split, going 'no chance for 60 miles' and not thinking of it any further.
I don't know what time could be lost on leg 1 to Billy to still be in with a chance.
From experience of others' schedules, Bob's calculator offers slack in the later splits (in case of explosion/implosion). This may suggest that his quick schedules tally up with Billy's time.