At my workplace we have a daily DMZ (De-Meetinged Zone) from 11 to 3. Since engineers tend to roll in btwn 10 and 11 and most product ppl work normal hours and leave by 6, you end up with a lot of meetings btwn 3 and 6. But at least they aren't methodically fracturing your entire day anymore.

Care is needed when scheduling. Standard parallelization stuff. If all your sub teams want to have sub team meetings (retro, planning, blah blah), try to parallelize those meetings so there's more time on the clock for cross team meetings. If you don't do this, manager schedule ppl will start violating the DMZ.

To manage Slack interruptions disable whatever your personality is distracted by. For me I turn off all notifs that aren't direct messages to me or @mentions. I hide chat rooms with no unread messages. And most importantly I don't keep Slack on top 24/7 on some second monitor. When ppl need me the client grabs my attention and I answer. The rest of the chatter can be read at my leisure. We use emojis in our engineering channels to make it easy to scan for action items like code reviews and we use threads for replying to ppl so the channel is like the top level view of a message board.

This is functioning fairly well with ~30 engineers at the org but i think we will need to more consciously manage the 3-6 window if we doubled in size again. Fred Brooks stuff, the 3 hour window is fixed but as teams grow so does the communication overhead.