sternone,
You can't 'demand' that this so-called instructor give you a briefing. Either he's doing it, or he's cutting corners. How are you going to know whether the 3-minute briefing he then gives you is what a good instructor - like Gemma's - would have given you or not?
A one hour lesson is always one hour's flying...though schools do vary as to exactly when they start timing. There should be extra time for briefing and the beginning and debriefing at the end. Some schools book one hour lesson in every two hours. Others book one hour in every hour and a half, and then it's a real headache for the instructor to get briefings done, but it's not impossible. That's what I meant when I said in an earlier post that they occasionally get skipped or skimped....and it's not always the instructor's fault. But if that's happening all the time, either the instructor or the school is taking you for a ride, and you need to go elsewhere.