One wonders here if the original text might have read “in the which time we might have enjoyed our possessions”. One could argue that due to the preceding “in the wilderness”, Oliver Cowdery accidentally dropped the second in the; that is, the original text read “in the wilderness in the which time”.
In support of the emendation “in the which time”, we note that elsewhere in the original text there are two examples of this phrase:
Alternatively, one could argue for an original “in which time” (based on the usage of the King James Bible, as in Acts 7:20: “in which time Moses was born”).
There are two other places in the text where one could argue that the preposition in was dropped because of its occurrence in an immediately preceding prepositional phrase headed by in. In both these cases, the 1920 edition supplied the seemingly necessary in (thus producing “in which”):
These two examples could be used in support of the earliest text in 1 Nephi 17:21—namely, the preceding prepositional phrase headed by in allows a following relative pronoun which to occur without an in, contrary to normal expectations in modern English. (For further discussion, see 2 Nephi 2:22 and Ether 13:15.)
Despite this evidence, there is textual evidence that directly argues for the earliest text in 1 Nephi 17:21:
We note there that the verb enjoy permits an adverbial noun phrase without a preposition—that is, we have a noun phrase acting as a direct object (namely, the word peace) and a second noun phrase (“a few years”) acting adverbially. In other words, we have “but a few years” instead of “but for a few years”. Similarly, in 1 Nephi 17:21, we have “which time we might have enjoyed our possessions and the land of our inheritance”. The direct object (“our possessions and the land of our inheritance”) is, of course, a noun phrase, as is the adverbial noun phrase “which time”, which occurs without any preposition such as in. The usage in 3 Nephi 6:16 should therefore make us cautious about emending the text in 1 Nephi 17:21.
Summary: Although the adverbial noun phrase “which time” seems strange, its use in 1 Nephi 17:21 is consistent with the adverbial noun phrase that the verb enjoy takes in 3 Nephi 6:16.