On this page (Twitch Help Portal) I found that I have 24 hours after campaign ending to claim reward:
If you are unable to claim the Drop in time, you will be able to claim it from the Drops Inventory page until 24 hours after the Drops campaign has ended.
I created Test campaign (from Jul 32 to Aug 8), watched stream, and got reward, but in Notifications I found out that I can claim reward after one week of campaign ending.
So where is the truth? Can user claim reward after 24h after campaign ending?