I think the new rule will be pay per post.
As in if you make 5 posts, you will be paid for only the 5 posts, the maximum you can be paid is 20 posts per week.
So In other words, there is no minimum.
That's what I understand from yahoo's update
Of course there is some confusion now.
Rules
Must make 25 posts per week
Rates will be changing as of Friday June 14th. Users will be paid a USD rate per post in BTC at a max of 20 posts per week.
Rest assured with the change in rules, Yahoo will also update the OP to erase the confusions and you all will know what to do in the next week from Friday / when the OP is up-to-date.