It's all very easy to say that 95% buses should stay to the timetable, but it isn't that easy. Buses have to contend with heavy traffic, road works, building of tram networks, football matches, Christmas shoppers etc, which all slow the bus down and knock it from its timetable. Jeeez it's almost made to sound like the bus companies and/or drivers do it on purpose.
I for example moved about 50 yards in 15 minutes in a school run traffic jam yesterday morning in Didsbury. The previous day the same road took me 30 seconds to travel down. How on earth is a bus supposed to stay on time in those scenarios? Moan moan moan.