A study at a company found that most meetings showed diminishing returns after 30 minutes, and little could be expected after 60 minutes  Moreover, the most productive meetings were those for which a clear time frame was established
For a meeting at the company to achieve maximum productivity, then, it needs to have a clear time frame and be no more than 30 minutes long
In general, a meeting at the company that is no more than 30 minutes long and has a clear time frame will achieve maximum productivity.