Caveat, I don't fly reserves (assuming that's what the "duty free" time period is reference).
You are paid the greater of what you fly or your line. We DO have minimums, even for reserve holders. Reserve lines pay a minimum of 6 tfp per duty period.
Here's our latest CBA (the reserve section is about 4 pages long, but this is a bit):
...
2. Reserve lines will be built with no more than sixteen (16) Reserve days per line in a thirty- one (31) day bid period, no more than fifteen (15) Reserve days in a twenty-nine (29) or thirty (30) day bid period and no more than fourteen (14) reserve days in a twenty-eight (28) day bid period.
3. Blocks of Reserve will not exceed four (4) days. Reserve lines may be built with a carryout block just as a regular line.
4. A minimum of three (3) days off between three (3) or more day blocks of reserve is required excluding monthly overlap correction.
...
So in a 30-day month, you are scheduled for 15 days of reserve (which pays a minimum of 90 tfp). The CA I am flying with next month has not flown yet in November, as he sat home on reserve and has not picked anything else up (or couldn't).
Again, I don't sit reserve, but when I did, it sucked. Re-routes, add-ons, RAP changes, ..., though it was a busy time here. I hear lately it's not as bad.
Not sure if this helped, Happy Thanksgiving!
PS We have GDO & TGDOs (Training / Golden Days Off). 1 per month maximum with a 7 per year limit. There are some restrictions, like Xmas, but we can still pick up on a GDO; the company may not use you without your consent. I have not used a GDO yet, but I do use TGDO, which are used to protect time you need / want off during your training months.
It's late, again, hope this helped.