I am trying to do the same thing. I change the timestamp in mongoDB, but it has no effect on the frontend.
Ps.: I changed the timestamp on topic, post and topics:recent.
Anyone can help me?
Right now there is no way to change the date of a topic through the forum itself, which means you would have to do the changes in the database.
Alternatively I can modify the rss plugin so it sets the date of the topics to the actual date from the rss entry instead of using the current timestamp.
Just in case someone will search for fast solution: if you are using redis-server as DB you can change timestamps with redis-commander:
npm install -g redis-commander redis-commander
And then you can access your database via http://yourdomain.com:8081