Roshen has been quoted on the Staff Post Tracker as stating the Beta will last 2 weeks. Will Sony be announcing in advance when the server will launch? I'm planning on cashing in some Vacation time and generally am required to give a week's notice before hand...
Sony won't be announcing it. I haven't seen anything about if Daybreak will give us lead time or not, unfortunately.
If we have advance notice of a couple days, I will be taking a couple days off. If not, I'm afraid I have a stomach bug/ate something bad/have a migraine.
Aristo quoted in General they'll be trying to announce an absolute date once they've got it pegged down.
Roshen said on reddit they'll give advanced notice. See this thread, scroll down to where Roshen responded to someone's question about advanced notice. http://www.reddit.com/r/everquest/comments/3580eg/progression_beta_server_live_now_ragefire/