You might be interested in the results of this email research:
"By taking a “typical” employee and making some hypothetical assumptions it is possible to determine the amount of time that can be saved through implementing the guidelines mentioned above. If an employee has set up the email application to check for email every 5 minutes then it is possible, if (s)he is a heavy user of email, that there could be 96 interruptions in a normal 8-hour working day. However, if the email application was set up to check for email every 45 minutes then the amount of possible interruptions is reduced to 11 per day. For example, if it takes on average 1.5 minutes to read and recover from an email and the employee is interrupted every 5 minutes, then this would only leave the employee 3.5 minutes before the next interrupt. However, if the employee was interrupted every 45 minutes and the emails had accumulated to a total of 9, then it would take on average 6 minutes to read all 9 emails and recover from the interruption. This would then leave 39 minutes before the next interruption, allowing the employee more time to get on with “real” work."
The research was completed in 2003 – I suspect the numbers become worse with the increase in email volumes and technology demanding our attention over the last few years. Net net, use Do Not Disturb or turn off your email notifications altogether.