It depends on whether people are colocated. For me, if the team is all on the same floor, I just don't do IM.[1] If they need an immediate response or one within 2 hours, they can just come to my cube. I don't mind being interrupted for these, because I've noticed people are more likely to think their problem through before getting up and walking - whereas with IM (and to some extent email) they're happy sending off a query without much thought. So I'm interrupted significantly less in personal than via email/IM.

If there are remote members, I usually respond to them on IM and try to ignore everyone else. This is to prevent colocated team members from having an advantage as I allow them to walk to my cube. I've toyed with having a requirement from them that if remote team members IM me, then they have to pick up a headset and talk live (similar to being interrupted in person). I haven't tried it yet.

Email in 36 hours is excessive for me - I think by the end of day is good for me.

Clearly different people have different preferences. My focus is to relieve the burden of always checking/being available. It prevents deep focus. I think this aligns with the author of the submission.

[1] Note that this is for IM in general. I've never used Slack - I've heard Slack is more than just IM so perhaps I would find a good use for it.