In our experience, registrations shouldn’t be opened too early, as it can lead to a high drop-out rate. That said, don’t start it too late either!
What really makes the difference is your communications strategy: effective communications will lead to quality user sign ups. You can do much better than a keyword campaign 1 week before the event!
Build a multi-channel communications plan which targets attendees who will hold a genuine interest in your content. With that in mind, we recommend you open registrations about 3-4 weeks before your event.