Another side note, doing a 4-day work week for engineering is a great and productivity boosting practice, but it shouldn't be seen as a carte blanche to not com

Another side note, doing a 4-day work week for engineering is a great and productivity boosting practice, but it shouldn't be seen as a carte blanche to not compensate them for after-hours emergencies. If you have a 4-day work week, then 32 hours a week is their normal full-time number of hours that you are compensating them for. When you ask them to go beyond this, you need to compensate them for their time.