It could all be up to the user.

A simple check box that reads "Auto Hide Flagged Posts?"
And when the user checks that box a menu below becomes available

A dropdown box with options like;
"Hide posts based on percent flagged"
A slider here to adjust percent from 1% to 100%
Another dropdown box that reads "Time frame" with options of
Any, 1d, 3d, 1w, 2w, 1m, 3m, 6m, 1y.
As well as an option to enter your own time frame.

An option to check a box that hides all flagged posts.