Map Pilot Flights

Both speeds are shown at the bottom of the speed selection slider. One is the maximum speed that will be allowed for the flight on the way out to the green dot and back from the red dot. The speed on the path depends on how fast your camera can take images, how high you are flying, the field of view of the camera and the along track overlap. 

https://support.dronesmadeeasy.com/hc/en-us/articles/211398963-Determining-the-Flight-Speed

It is also possible that it is being slowed down due to lack of light. This happens pretty regularly in the winter in the northern hemisphere but can be turned off (it is there to protect your data from being unusable). 

https://support.dronesmadeeasy.com/hc/en-us/articles/209866886-Light-Based-Speed-Adjustment