First, after he hears his brothers express regret for how they treated him:
They did not realize that Joseph was listening, since they [had spoken to him] through a translator. Joseph left them and wept. When he returned, he spoke to them sternly again.
Later, after Joseph sees his younger brother, Benjamin:
Joseph rushed out. His emotions had been aroused by his brother, and he had to weep. He went to a room and there he wept. He washed his face and came out. Holding in his emotions, he said, 'Serve the meal.'
In this week's Ten Minutes of Torah, Rabbi Charles A. Kroloff writes about Joseph's inability to cry in front of others (an inhibition he will overcome next week) and discusses why we shouldn't be afraid to express emotions through tears. Click here to read his commentary.
The Eternal One spoke to Moses, saying: "Command Aaron and his sons thus: This is the ritual of the burnt offering: The burnt offering itself shall remain where it is burned upon the altar all night until morning, while the fire on the altar is kept going on it." - Leviticus 6:1-2