Day change (DC) is at 00:00 in e-Sim time (CET/CEST).
You can see the current e-Sim time at the top left corner of the page.
At day change you will gain 50 health. Your food and gift limit will be reset to 10, 15 if you own a house and/or estate. If you are in a debuff of Extra vacations (food) and Extra spa (gift) your limits will not reset.
After day change everyone will be able to train, work and fight again.