Based on past experiences, I personally would wait a couple of months after stopping, as long as you're asymptomatic. 300 is actually not that high of an elevation, if acute (even though it's about 6X high end of normal), but you want to make sure it goes down when off orals. I'd do the typical LFT bloodwork (AST, ALT and alkaline phosphatase) with the CPK. If you're training on a regular basis, even with a few days off it will likely be elevated. If the CPK is sky high, it would explain elevated AST and ALT. Remember that these are just indicators, and your doc will determine if anything concerns him. You'll probably be okay after the liver gets a rest.
BTW, are you checking stool color when you drop a deuce? Light colored stool (khaki/clay to white [yes, white] colored) can be an indication of a biliary obstruction which could be caused by liver problems. Just something to check periodically, even when everything else looks good.
If your elevations are chronic, your doc may script you an ultrasound of the liver and/or refer you to a gastroenterologist to check you out. Only then are you getting closer to a conclusive answer. I have a feeling that when you're off the orals and you see your CPK numbers, everything will make sense and you'll be G2G. Good luck!