Someone should not stay in a hot tub for more than 20-30 minutes at a time. It is important that you consult with your general physician if you are taking any medications are pregnant or have any health conditions as to whether you should use a hot tub.
Yes! Most people should not stay in for more than about 20 to 30 minutes. Any longer and you risk becoming overheated and/or dehydrated. The absolute upper limit for use is an hour at one time, but that is pretty unnecessary and you should drink a good bit of cold water if you were to do so.