How long should brainstorming sessions last?

It's 2017 and project managers still freak out every time they have to calculate how long it will take the creative team to arrive at a solution for the client's brief. We have all been there. It's an endless fight. So, is it impossible to calculate how long the creative process should last?

Well, short answer; it's complicated. Long answer; you can take into consideration these two factors.

Better shorter than longer sessions
When it comes to the actual brainstorming sessions, it's better to plan a couple of short sessions than a long one. In that way, you can refresh your team's energy, make some pause and order ideas in your head. Each session could last from 1 to 3 hours.

Spend more time only when it's needed
If we had to make a formula, it would like something like this: t (time you spent brainstorming) = i (level of innovation desired) - p (pressure from a deadline, budget, resources, etc). That means, the more innovation and less pressure you have on a project, the more time you could spend ideating, and vice-versa. If no innovation/originality is needed, you should be more efficient and focused.

The time you'll spend ideating will always depend on the nature of the project. Next time you need to make some predictions, try to keep in mind the previous factors in mind.