What the Bible says about Thursday Evening Begins Preparation Day
(From Forerunner Commentary)
Exodus 16 begins the miracle of the manna. Instructions were clearly given to Moses, which he in turn passed on to the children of Israel, about what they were supposed to do on Friday. They were to gather twice as much on Friday, because they were not to gather manna on the Sabbath day.
This principle is still in effect. We should not say that we do not have the time to prepare. If we lack the time to prepare, something is wrong with our use of the other six days of the week. Maybe our habits of organization and priorities need to be changed. The preparation day for the Sabbath begins at sunset on Thursday (since Friday is the preparation day, and the day begins at sunset). Meals can be prepared ahead of time, even including leafy salads. If they are prepared properly with fresh ingredients, they will be nice and crisp on the Sabbath day, twenty-four hours later. God says to prepare because He does not want ordinary weekday work done on the Sabbath day.
John W. Ritenbaugh
Sabbathkeeping (Part 4)