One way to form a habit is to reduce friction.
Want to eat more fruit? Always keep bananas on the table. My wife will kill me if I forget to buy bananas every week.
The opposite is true too: introduce friction to stop a bad habit from forming.
If you don't want to be responding to Slack messages 24/7, introduce a delay and batch replies. This stops a habit from forming from whoever is messaging you.
This is true for yourself and for your team.