[devo-x-lie]

You are right, having this one rule for all will not make a lot of sense. But I take it just as an example, in my place the nature of our team and work is such that this SLA can and is meet without any problems.

Looking at my last place, it's more like a 24hour SLA and that would still be ambitious in some case.

Maybe try to experiment with this number and see if you can agree on something more optimal? (There is nothing hard / time consuming in having a quick check in your emails and messages once per hour. I hate this idea of people working in teams but always wanting to not be disturbed ALL the time.)