@Bran I have also read that it goes to baseline after 8 hours, I usually workout in the morning so I target to lower it again with my night doses and consume plenty of protein to give the body something to work with while I recover in my sleep.
I'm not sure if working out certain groups would have a systemic effect on myostatin levels. I do a Pull Push Legs routine over the week, around 1 to 1.5hr daily.