Does anyone care to explain how two buses departing from the same stop, traversing the exact same route, have two different estimated times of how long it takes to get from Rowlands Gill to Newcastle?

http://liners.nexus.org.uk/20011.pdf

According to the timetable, service 45 takes 29 minutes while service 46 takes 35 minutes. Service 47, which goes a slightly different way, takes 30 minutes.

I didn't really want to put this in the 'Life's Little Mysteries' thread but perhaps I should have done!

I wonder if there any more examples of this timetabling anomaly.

(Yes, I know it's Nexus and expect nothing less!)