Not exactly what you're asking, but even the plug in category can expect around 14 days off. Depending on days in the month, line value, and number of reserves it varies, but 13-15 are the possible reserve days off in a normal bid month. There is effectively no limit to number of reserve days in a row either, so you can put the off days in a single block without too much trouble. Reserve sometimes does go senior and sometimes the junior pilot in category will hold a line.