How long did the signature of the circle of friends disappear after it was hacked?

In this case, the signature will not disappear.

If you just add someone to the blacklist without deleting friends, then WeChat friends can still see their friends' signatures. The signature of the circle of friends will disappear only if the other party deletes the friend from the friend list or deletes the other party from the friend list. Wechat blocking is a one-way deletion of friends, not a deletion of friends, so the signature of friends circle will not disappear.