How long should I stretch for in general ?

Studies do support that range of motion can be increased by a single twenty to thirty second stretch for each muscle group most days of the week. However, some people may require a longer time for various reasons, for example the elderly, during rehabilitation and prior to participating in a serious sport. There is also logic in the fact that research also supports the idea that the optimal duration and frequency for stretching may vary per muscle group.
Research supports thirty seconds per stretch as part of general conditioning to improve your range of motion.