Calf raise frequency?

 I realize the recommended frequency for the stretch series is once per week but I'm a long way from the prescribed 60 reps of each in the calf raises. Is there any problem with practicing them more frequently, like two or three times per week?

I don't think that there is a problem with this.. Try it, if it helps you progress faster towards sixty reps so do it, if not don't do it..

It should be fine.  The prescription for a weekly stretch session applies to the entire session, not the individual elements.  Calve raises can be done with some frequency, depending on individual development.  Ballet dancers do large volumes of them (eleve, releve).  I have recently tried some adult ballet classes and you are constantly going up and down at the ankles.   There was an interesting article about a fellow trying daily raises on T-nation.  I forgot the name of the author, but a search should work.  

We used to do hundreds of weighted calf raises(40ish lbs) daily in drumline, including marching sideways and backwards, which is basically single leg calf raises. It SUCKED the first week. Then we developed the calves of Greek gods. It won't hurt, calves like high volume.

I literally came online to ask this very question. I wonder how the OP got on.