Slack has a scheduled do not disturb feature, you can set a period every day when you don't want to be disturbed by notifications. If someone DMs you, Slackbot tells them that you're in do not disturb (and gives them the option to "poke through" and notify you anyway). I work for a company with offices in both Europe and US (and people travelling frequently between them, so you don't always know where they are), and this feature is broadly used.
"and gives them the option to "poke through" and notify you anyway"
Yeah...this is why I close down slack when I don't want disruptions. There's no point in a DND if others can do it anyway. It shouldn't be an option. If someone at work has an emergency and needs to get hold of me, they can give me a phone call. Non-verbal communications have a tendency to be abused, but the reality of actually having to have a conversation with the person you're disturbing means only serious calls seem to get made.
