it was monthly before
This works out well for me, since quite often I would have a week or two mid-month where I don't play much, and would struggle to put in the volume to make the target.
from the announcement email
Hi VorpalF2F,Maximize the rewards you earn and get 40% extra in rakeback while playing your favorite poker games – only with the Weekly Poker Challenge.
Ready to win an instant cash reward of $16? Open your Challenges Window and discover your weekly rake target. Reach your rake target by 23:59 ET on Saturday to unlock a $16 cash reward.
You’ll earn 5 redemption points for every $1 you pay in rake or fees playing most poker formats. And you’ll still earn reward points towards your next PokerStars Rewards Chest while you play.
There are no earning requirements or restrictions to claim your rewards. You can complete the Challenge a total of two times during this period.
VS
beside "Open a new ticket"