We work on our desires during the night, in the darkness of the exile, having no strength. While still in the darkness, we prepare ourselves to greet the morning, meaning we find the desires we can sacrifice.
We are not talking about the physical sunrise or sunset, nor do we refer to pieces of flesh of sacrificial animals. We speak only about the use of the Light of correction in which a person can see himself as a sacred vessel.
In other words, a person will reach the Temple, come to the burnt-offering altar, and become ready to work with his desire by raising it to the level of bestowal. The elevation of the parts (“pieces”) of our desire to the level of bestowal is what is called “offering.”
From the 1st part of the Daily Kabbalah Lesson 4/25/10, The Zohar