The timings are an estimate only, using a modifed version of Naismith's Rule. Your actual time will almost certainly vary.
Ensure you plan for the slowest member of the party, not the fastest! No allowance is made for stops for rest,
photographs, navigation, crossing obstacles or problems. Ensure you leave a generous safety margin if you have to complete the route by a specific time.
Factors such as adverse weather, difficult ground, and carrying loads will increase the time taken.