Believe it or not stretching doesn't often get a good rep in the rehab world. When it comes to management of injuries and dysfunctions it is regularly overlooked by strengthening and 'functional' or stability drills. Heck even when discussing exercises for flexibility the current trend is to recommend strengthening over stretching.
I personally find that people are quick to throw the baby out with the bathwater. I can see why though, stretching is only shown to reduce risk of injury by 4% compared to strengthening at 69%. That means it is easy to emphasise strengthening over stretching when it comes to injury reduction.
But that doesn't mean that stretching isn't important. Even though range of motion CAN be improved through strengthening, stretching is still a feasible method of increasing long term improvements in range of motion and flexibility.
A systematic review found that stretching between 5-10 mins per week may be your best bet at making long term improvements in flexibility. It is further suggested that trying to break this up over more frequent sessions ie 2 minutes a day for 5 days a week may be better than one 10 minute session a week.
Additionally, stretching for under 5 mins still created some improvements at +16% but as expected a longer duration such as 5-10 mins was more effective at +23%. Interestingly stretching for longer than 10 mins had no additional effect. So 5-10 mins is where your money is best spent.