Uncover and grind meal
'To uncover' signifies adulterating the goods of the Word, and 'to grind meal' signifies falsifying its truths.
(References: Apocalypse Revealed 794; Isaiah 47:2)
Day
Like other descriptions of time in the Word, "a day" or a number of "days" describe a spiritual state rather than our natural concept of time. A spiritual "day" describes a state of mind or a state in our relationship with the Lord rather than a 12-hour or 24-hour span of natural time. "Day" describes a state in which we are turned toward the Lord, and are receiving light (which is truth) and heat (which is a desire for good) from the Lord.