I don't think so. This is from personal experience, but when we moved from one city to another and had to rent while we sold at one end and sorted out somewhere to buy at the other we rented a house on a six-month agreement with a clause to say that after three months either party could serve a months notice. This was through a well-established letting firm in the town. We left after five months and everything was as per arrangement. If someone is trying to tell you six months is the minimum full stop then they're probably trying it on.