Recommended background music for this post: This music video of
the Satmar Rebbe singing Psalms 42:3 [Hattip: Reb Ariel]
HaShem told Abraham that his descendants would be slaves in Egypt for four-hundred years. However, even if one adds all the years of Kohath, Amram, and Moses together, the total does not approach the four-hundred years prescribed, in fact, the total amount of years that the Jewish nation spent in servitude in Egypt was merely two-hundred and ten years. The question then arises: Why were the Jews exiled in the land of Egypt for only two-hundred years and, according to some, they were only indentured as slaves for one-hundred and sixteen years, instead of four hundred years like HaShem told Abraham? Furthermore, the Torah testifies twice that the Jews stayed in the land of Egypt for four-hundred and thirty years. How is this reckoning to be reconciled with the simple calculations? The Midrash answers that Ephraim and Manasseh were in Egypt for five years before Jacob and the Jacobean family descendant to Egypt from the Land of Canaan and the Israelites worked in Egypt day and night for two-hundred and ten years. In adding the total ten years that Ephraim and Manasseh lived in Egypt with the doubled two-hundred and ten years that the Jews worked in Egypt (because the day and night are to be counted separately), one arrives to the grand total of four-hundred and thirty years.
The Satmar Rebbe of Kiryas Joel, Grand Rabbi Aharon Teitelbaum, says that this is a proof that the Abrahamic family before the Sinaitic revelation had the status of Jews, not Noachides. Had the Israelites had the status of Noachides, then they would have had the status of Canaanite Slaves under the Pharaoh and would thus have been required to work day and night. However, since day and night were counted separately in the reckoning the years of slavery, it must be that the Israelites had the status of Jews, and were thus Hebrew Slaves who are only required to work during the day, not at night. Similarly, when Moses added an extra day to the three days of preparation for the giving of the Torah at Mount Sinai, he wanted there to be three periods of night-followed-by-day in order to insure that all the Jews were properly ritually pure. However, HaShem had only originally commanded so for three periods of day-followed-by-night ("today and tomorrow"). The root of the "disagreement" between HaShem and Moses is whether the Israelites had the status of Jews or Noachides. Had they been Noachides, three periods of day-followed-by-night would suffice for their purification because for Noachides the day precedes the night; while for Jews the night precedes the day. In the end, HaShem concurred to the opinion of Moses and decided that the Israelites then had the status of Jews, not Noachides, so He allowed the extra day of preparation and switched the commandment to prepare to "three days".
The Satmar Rebbe said there is another very fundamental combination of answers to explain why the Jews were only slaves in Egypt for two-hundred and ten years, instead of four-hundred years. One answer says that since the Talmud says that sanctification can break the bonds of servitude, so even though the Jews were supposed to be slaves in Egypt for four-hundred years, since they sanctified themselves, they were liberated early. Another answer says that the extra years which the Jews did not suffer in Egypt are scattered within the subsequent exiles, and the Jews are still "paying off" the four-hundred years of servitude. By combining these two answers, the Satmar Rebbe said that one can say that if one sanctifies himself through the learning of Torah and properly serving HaShem, he can avoid the clutches of the current exile and merit to see the coming of the Messiah and the rebuilding of the Third Holy Temple in Jerusalem, may it come speedily and in our days: Amen.
 See Genesis 15:13
 See Rashi to Exodus 6:18-20
 Sifsei Chochmim to Exodus 6:16
 Exodus 12:40 and ibid. vs. 41
 Pirkei D'Rabbi Eliezer Ch. 48
 In a speech delivered on 24th Teves, 5767
 Bava Kamma 87b
 Although Rashi to Deuteronomy 15:18 and Kiddushin 15a say that a master can make his Hebrew Slave work at night by mating him with a Canaanite Maid, that is not necessarily called "work" in the legalistic sense.
 Yevamos 62a
 See Exodus 19:11-15
 Shabbos 86b
 Exodus 19:10
 Based on Genesis 8:22
 Based on Genesis 1:5
 Exodus 19:11ff
 A similar discussion regarding this topic can be found in the Chasam Sofer: Toras Moshe to Exodus 19:10 written by Rabbi Moshe Sofer (1762-1838)
 Yevamos 46a