I'm in the middle. I have developers that work whenever they feel like it, and they email me with questions at all hours. I like to be there for them when I can (but I don't feel bad when I can't).
I've set up my email client on my phone, so that it only notifies me if one of my developers emails me. I use the VIP feature of Samsung's email client, which seems to be unique to that specific client, since I haven't been able to find another with it. I can check the email (if I can), and decide to answer right away (if I can), or just snooze the notification for later.
Everyone else can KMA after hours. Or text, if it's an emergency - but they better say what the emergency is in the text, or they may not get a reply.