What does research suggest as a best practice for how much time should be spent in initiating and planning activities for projects

What does research suggest as a best practice for how much time should be spent in initiating and planning activities for projects

What does research suggest as a best practice for how much time should be spent in initiating and planning activities for projects? Do you think that estimate is realistic? Why or why not? How does spending more time on planning help reduce time spent on executing? Give examplrswes of how this has worked on real projects.