3 year partner and shift supervisor here:
1. It typically applies to any blend that is available at ***all*** retail locations (the core blends like siren's, veranda, Yukon, etc. as well as the seasonal and special release such as Christmas/Holiday, Casi Cielo, etc.) but the ***all*** is very relevant, as the Reserve stores and certain markets have blends and releases that are not eligible for partner markouts, such as stores in Hawaii that sell Kona coffee or the Reserve Vietnamese Du Lat, etc.
2. You can get it on your day off, and at other stores as well. If you use your partner numbers you might have to show i.d. in order to verify yourself, but if you use your partner card or
$1, this won't be necessary. I should also mention, you don't have to be in Starbucks dress code to just get your coffee markout, as you are essentially only acting in the capacity of a customer while doing so.
Edited to hyperlink to another comment about linking the partner card