Litchi waypoint mission flight time calculation

I did not find that topic with the search function, so here it goes:

I have flown waypoint missions with my DJI Mini (where flight time was always less than calculated time by the app) and now I want to fly one with my new DJI MA2. When I plan the mission with Litchi the app calculates for a 13.3 km roundtrip 27 minutes of flight time even if I set the cruising speed at 39.9 km/h (which is within N-mode capabilities). This is strange since mathematically flying 13.3 km with 39.9 km/h should take exactely 20 minutes! Why does Litchi then show a total flight time of 27 minutes for that waypoint mission?
20 minutes is very much doable with a full battery - 27 minutes might not be!
I have looked at some Youtube MA2 review videos and they confirm a max. total flight distance (not to be confused with max. range!) in excess of 15 km (DJI gives 18.3 km if I remember correctly).
So why the miscalculation of the flight time by the app and shouldn´t 13.3 km be within the capabilities of the drone? Has oneone already flown such a long waypoint mission with the MA2 and how did it go?
Thanks for some input!

Hi Cliff,

This topic does come up from time to time. Litchi builds in some extra time into their calculations to allow for takeoff and returning to home. So, the time LItchi shows is from takeoff to landing (roughly).

Why don’t you think that the drone accelerates and slows down, it takes time.в

I think if you watch the drone speed on the screen, you’ll see it slow down several times for turns, approaching waypoints, and to take photos.

Hi Glenn,

What you say may be true for straight-line missions where you are taking photos at the waypoints. However, for missions with curved turns (normally used for shooting video) the drone will maintain the “cruising” speed throughout the mission unless you have custom speeds set at the waypoints.