[lizard]

There are almost certainly different approaches depending on the environment and situation. But, especially if this is a "culture" problem one of the best fixes I've found is to make shorter meetings with a defined agenda, such that you can always pull out a, "I'd love to take this offline, but we need to get back to..."

I've personally found you should almost never need more than 30 minutes unless you specifically want to get into rabbit holes. And if you do need more than 30 minutes, it's probably better to split it into multiple sessions of no more than 30 minutes anyways to prevent this from happening. If you still have this problem at 30 minutes, shave 5 from either side (or both), which you can even use the excuse of giving time to transition between meetings.

That's not to say you shouldn't genuinely allow room for brainstorming, but if you're going to take an entire room of peoples time, make sure it's something the room agrees is worth discussing and find another time to do it instead of getting sidetracked now. If not, offer some 1-on-1 time, and move on.