Hi Don,
How are you uploading a track, are you first saving it out as a .CRS file? Remind me what GPS you have.
You might be able to adjust the speed a bit by decreasing the number of points in your track. If you take it down to 25% of the total number of points you might get some more reasonable speeds.
I don't think a precise way of fabricating times is worth effort, but maybe an option to go with a preset speed would make sense.
Thanks