According to Visa Services at Duke University the amount of time a person has to wait to take a citizenship test depends on LPR status. If the LPR status is marriage based, the waiting period is three years. An LPR status that is through any other basis requires five years.
Visa Services at Duke University also states that the process for citizenship can begin approximately one year before the three to five year waiting period. In addition, individuals have the option to begin the process but not complete it, specifically not taking the Oath of Allegiance. Once the Oath of Allegiance has been taken citizenship is considered permanent.