CX season running. What days?

What days of the CX specialty plan would you incorporate some running? I know that there is big debate on what type of running (if any) you need to add to cx training and it has been discussed on the podcast. I basically do 0 running throughout the year, so my legs really feel any time off the bike during a race and I have been having issues with calf cramps.
I feel that if I could at least get them used to some running, it might help, just trying to figure out the best way to fit it into the training plan.