We make builds almost every weekday evening. Our internal and external testers play those every day. They are no different than what we would release to the public. It is just a matter of, are the features working the way we want and the nasty bugs fixed for release to the public?
Content lock has not happened as there are things we are adding that are still in progress. We don't really do a 100% content lock anyway. Something could be added a month or week before experimental if it fit in with our plans.