Mark,
If you are talking about the SoG (speed over ground), then you will need to have a NMEA connection in order to interface your GPS signal so that it can display that if you are using this software under way. That data will be repeated to software, however, only if you have that NMEA interface. Below I have a link for the manual if you have more questions about setting up a NMEA interface.
If you are talking about the route time that it may estimate for you, I am not sure how you can change your rate of travel. I tried to see what I could come up with in the manual
(right click here and hit Save Target to save the Raytech Planner manual) but I couldn't find it. I would suggest giving Raymarine a call to see if they can help walk you though any steps if it is possible. They can be reached at (800)539-5539.
Sorry I couldn't be much more help, but let me know if you have any other questions. Thanks, and have a great day,
RayMarine planner 
