In 24 hours, that's 23.3% less posts.
In 48 hours, that's 18.6% less posts.
In 1 week, that's 15.9% less posts.
In 2 weeks, that's 18.6% less posts.
In 3 weeks, that's 22.2% less posts.
OP updated.
The reduction in total posts went up again!
If I ignore the one week before and after theymos' changes, and only look at the number of posts made a week earlier and later (so posts made from September 3 to September 10, and from September 24 to October 1), it went down from 355933 to 280633 posts. That's a 21.2% reduction.
If I ignore the two weeks before and after theymos' changes, and only look at the number of posts made two weeks earlier and later (so posts made from August 27 to September 3, and from October 1 to October 8), it went down from 367037 to 260330 posts. That's a 29.1% reduction.