In my company cpt say "Attention Crew Attention Crew!" That means, girls (and/or lads), remain seated and wait for instructions... It is always told to them that there might elapse a few minutes from attention crew to EVACUATE or "disregard attention crew" because the pilots are evaluating the need of an evacuation and also because once the desicion to evacuate has been made, there's a checklist to read. If we dont make any announcemente the risk is that they might think that something happened to us and make their own desicions...
What experienced cabin crew usually say (specially those who have been on a rejected take off) is that from the moment they hear the "attention crew" announcement until something really happens, the cabin crew become quite nervous and minutes stretch so much that it seams like ages before they hear something else...