Based on ‘Naismith’s rule’, the basic walk time for a route can be estimated using the typical 5km/hour (3mph) walk speed over flat terrain and an extra half hour for every 300m (1,000ft) of ascent (average fitness).
Your route, measured in km, is divided by 5 (km/h) to get approximate time in hours and then you add an extra minute for each 10m ascent of your climb ( i.e. 1/2 hour for every 300m climb) and an extra minute for every 30m of descent when the descent is continuously steep.
See www.walkingenglishman.com/walktime.aspx for a simple example of how to calculate your walk times and for a more detailed calculation which has variable walking speeds for flat terrain and ascent depending on fitness and known pace, etc. This could also be applied to cycling but is a little more difficult to calculate.