If you mark a map using distance or time, they are still TIME markers and a student at least should be learning to go from watch to map to ground. BH - Not using them as time points may suit you, but it is not really the way to teach ab initio, and even if you have that many variables, IMHO a student should still be learning time, map ,ground, you just make it that he has a wider time band to operate in.
nb. I don't really see how your variables change so much unless it is either poor planning, poor flying or you are actually doing a job where you are changing your plan. I fly many thousands of miles and usually arrive within minutes of my planned arrival time!