Configure your SMTP server so that any email sent after 8pm is only sent to the other party at 7am; with a similar rule during weekend. [I am not sure how to perform this in practice with common SMTP servers, but there is not technological barrier here]
So employees can still "get work done" after hours, but they don't receive new tasks. In case of emergency, use the phone.
NYState could implement this in law. Emails sent at night to employees that are off-duty (i.e., not explicitly paid for night hours) should be blocked until the next morning. Much easier to implement than GDPR :)