I don't know of any programs that have a hard and fast rule about it, although as Carlene mentioned it's strongly encouraged by longwood for instance.
Not one program has asked me about when my CS scores will be in other than longwood (took CK in time for hte scores to go out with on the first date you could submit ERAS)
I and several of my friends have been told my various PDs that it's very case specific. I.e. if you're an FMG,better have everything in before ROLs are due. If you've failed step 1, better have them all in. If step 1 was marginal, better have it all in.
If you scored a 99 on Step 1, they're not going tobe as concerned.
And they're really not going to be concerned if you've at least scheduled CS early enough that if you DO fail, you have time to retake it and getscores before intern year.
Obviously this does not apply for EVERY program, just most of the ones I and my friends have talked to about this issue.