“in the day.” The Hebrew does not have the definite article, and “in the day” refers to a period of time. God did not make the heavens and earth in one 24 hour period. This is the same wording in the Hebrew text as in Genesis 2:17 (see commentary on Gen. 2:17).
“Yahweh.” Genesis 2:4 is the first use of the personal name of God in the Bible. The Hebrew name of God consists of four consonants and no vowels, and there has been a long-standing debate about how to spell it in English and how to correctly pronounce it. The four Hebrew letters are yod he vav he (transliterated as YHVH). The REV uses the English spelling “Yahweh,” which is used by many scholars in their commentaries and in some English Bibles (cp. HCSB; NJB; The Jerusalem Bible; Rotherham's Emphasized Bible; New European Version; The Complete Bible: An American Translation; The Expanded Bible; Ancient Roots Translinear Bible). No one knows exactly how YHVH was pronounced, and it seems that if God really cared that people pronounced it exactly correctly, then He would have done much more to make the pronunciation clear to us.
As for what the English versions do with the translation, most use the word “LORD” spelled with capital letters, but “LORD” is a title, not a name and the title takes the focus away from God’s use of His name since there are other Hebrew words properly translated “Lord.” The name “Jehovah” is used in some Bibles (cp. the 1901 ASV), but there is no “J” in Hebrew (although the early English translators used the English “J” for the Hebrew yod, and thus producing the English translations “Jerusalem,” “Joshua,” “Jeremiah” and such as that. Some modern scholars think that YHVH should be translated into English as “Yahowah” or something similar, but since the exact pronunciation of YHVH is unknown, and “Yahweh” is accepted in English versions and scholarly works, there is no compelling reason to use an unusual and seldom-used spelling for God’s name in the REV in an undocumentable attempt to be more correct.