Annulment is a legal process that results in a marriage getting void or null. It is not like divorce in which the two individuals are claimed to have had a marriage and then divorced. When two people get an annulment for a marriage, it is as if they never got married. Usually, the process requires witnesses from both sides who could provide evidence of reasonable excuses why the two individuals were not supposed to get married in the first place. Then the two individuals themselves have to testify in front of a lawyer that they do not want their marriage to exist. Most commonly, the reason or excuse behind an annulment is said to be fraud on part of one of the individuals. How long the entire process takes depends on how long the couple takes to get witnesses and evidence to qualify for annulment. It usually takes about a week or two.
There is no fix time period but the norm is approximately 16 months. If the petitioner is late gathering the required documents then the annulment will be late.