The mod implied that to be able to receive the activity reward, you must be 7 days of age on the Monday on which the reward week is reset, which means it can take anywhere from 7 days to 13 days 59 min 59 seconds depending on when you joined the group.
GNW, on the other hand, is just 7 days, thus can be unlocked sooner.
Personally, I have no idea how it actually work and how it is supposed to work, but it may or may not be a bug.