1) TED/TEDx format: 18 minutes maximum, thats it. If you sit in the wrong talk, you know thats its finished after 18 min max. In the usual format it will take you 45 minutes.
Format: A suite of short, carefully prepared talks, demonstrations and performances on a wide range of subjects to foster learning, inspiration and wonder — and to provoke conversations that matter. (The typical presentation should be an 18-minute talk by a single presenter. No talk should exceed 18 minutes. No panels. No break-out sessions. Usually: No podium.) You may not pay your speakers to present.
see the full rules here: