It is stable enough to be used in development - don't upgrade a "live" or production site. When it is ready for a production site it will no longer be beta.
Just to add: Please make sure you test Jamroom 6 on your DEVELOPMENT site before upgrading ANY "live" or production site to Jamroom 6. This is FIRST beta of Jamroom 6 and there are likely to be issues that could have an impact on how your site works.
We want to find out any issues and fix them up before you upgrade your live site.
That would be part of the new Timeline updates - give it time to update your existing timeline entries (which is done by a queue worker) then reset caches - let me know if that helps.