I hate ride schedules - I (personally) find them demoralising and demotivating.
Having said that, I plugged some random numbers into a spreadsheet for the Border Raid last weekend, and I was greatly amused to note afterwards that my spreadsheet matched my finishing time to the minute. I didn't look at it during the ride.
Anyway - my point is that schedules and expected times are fine, but as VM says, you need to be flexible and go with the flow of the ride.
On one of Dave Atkinson's rides from Richmond (Yorkshire), I met a guy named Gerald, who was briliant, an experienced duathlete, and he explained to me the notion of Three Targets, i.e. you'd go into an event with a Dream target (e.g. 600 km in 30 hours), a realistic target (600 km in 37 hours), and an acceptable target (600 km within the time limit). Very useful for audaxing