The problem with this approach is that you need to calibrate your personal speed or speed in actual terrain or current load. You will move much faster on a day trip with a light load than on an overnight trip with ski mountaineering gear or a multiday camping trip in summer.

The next simplest thing is to use a rule of thumb. Calculate an hour for every 2 miles/3 kilometers and one hour for every 1000ft/300m—this planning approach you can now use without a computer. If you are planning from paper maps at the hut or tent, you can use this calculation, and you can adjust distance/h and elevation/h based on your condition, terrain, or amount of gear you are carrying. You can also get distance and elevation differences in your track by clicking it and selecting terrain stats. This will also tell you the planned route's slope angle, aspect, and vegetation.

Example: on the picture below distance is 1.3 miles, and the elevation gain is 1175ft. Travel time is, therefore, 1.3/2h for horizontal and 1175/1000 for vertical movement. Count these together, 1.3/2+1175/1000=0.65h+1.175h=1.625h=1h 50min (slight rounding up, no sense planning to seconds)

The most sophisticated way to calculate travel times is using the Munter tour plan formula. In the Munter formula, units are given to distance and elevation difference. Every 1km or 0.6 miles gets one unit. Every 100 meters or 300 feet of elevation change get one unit. The total of units is divided with a divider selected by mode of travel.

If you are using the munter formula for climbing, you can estimate 45min for every pitch of multi-pitch climbing and 350-600ft per hour for 3rd-class to easy 4th-class scrambling.

Adjusting the Munter formula: If you are a route finding and skinning up on the dense trees in a deep snowpack, you might adjust the divider all the way down to 2. If you are skiing down with a small group of strong skiers, you can adjust the divider to 16. In general, if you find your time estimates to be too optimistic, make the divider smaller, and if you are faster than your time estimates, make the divider bigger.

For safety reasons: always round your units up and add 1 hour to every 6 hours of travel for brakes etc. On planning, you will have to brake the travel on legs when you time plans anyway. Now you are braking route typically to uphill and downhill. these legs can also be used for making notes about navigation. Below picture of a slightly more complicated plan.

Also, instead of calculating these by hand, you can use an app called GuidePace, which will calculate your time.