Have you considered setting up a rule using the Snooze feature[0]? Using this it should be possible to delay all incoming work email until a time that is suitable for you.

[0]: https://www.fastmail.com/blog/fastmail-snooze/

Edit: If you want your work emails to arrive only during work hours and otherwise delay them, you can use a Sieve condition in your email rule similar to this:

  anyof (date :value "lt" "date" "hour" "09", date :value "ge" "date" "hour" "17")