Hi there Davide, if you view your route you can see the total trip duration directly below the search bar.
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If you're planning a multiday trip I'd advise just building the route as one route and then using the "split route" option to cut it into different parts.
Tip!
A great example of amazing multiday trips that you can both use as basis for your own routes can be found at myrouteapp.com/library. These routes already include information, stops and everything you might need.