In The Great Gatsby, how long has it been since Gatsby and Daisy have been together?
Jordan recalls for Nick how Daisy and Jay met in chapter 4. The year was 1917. Though the reader doesn't know yet that the current year of the story is 1922. Next this five year span of time is mentioned specifically again in chapter 5. Nick has invited Daisy to his house for tea, at Jay's request. Daisy and Jay see each other and Daisy comments that they haven't seen each other "...for many years." Jay says, "Five years next November." Jay has carefully noted the time which tells the reader how important that passage of time was. Later, in chapter 6, Jay recalls to Nice about the first kiss that passed between the two of them, "...One autumn night, five years before, ...".
Coincidentally, it was five years that Jay Gatsby spent with Dan Cody transforming from James Gatz into Jay Gatsby.
In Chapter Four, it is revealed that Daisy and Gatsby have not been together for five years. Remember that the novel is set in the summer of 1922 and Gatsby first met Daisy in 1917 in the town of Louisville in Kentucky. At that time, Gatsby was a soldier who became separated from Daisy when he was deployed overseas. According to Jordan, Daisy tried to go with Gatsby but was prevented by her mother.
While Gatsby was away, Daisy met and married Tom Buchanan. When Gatsby returned and found this out, he dedicated the next few years to amassing as much wealth as possible so that he could win Daisy back. For him, time is irrelevant: his mission is to be with Daisy and he will do everything possible to make this happen.
Since Gatsy first met Daisy, five years have passed because he has been away at war and then involved in business to make the money he believes he needs to win Daisy's love. Not until he is rich does he arrive at West Egg. In the meantime Daisy has married Tom Buchanan and had a daughter, Pammie.