“Before I turn my attention back to my work, I might decide to take a quick peek at my email, and while I’m doing that, notice that I’ve missed a call and three texts. If I answer just a few of these incoming communications, it may well be longer than 23 minutes before I get back to work.”
As relevant to this point
Formal is a interruption free messaging app delivers messages only three times a day in batches.
Learn more about how it works at https://www.formalapp.com
In Formal, There is no need to turn off notification or closing the app is needed. (For example, you can keep open the app to search some early messages)
Disclosure: I am a developer at Formal. Sorry to post a promotional response.