In Episode 3 - "Sasuke and Sakura: Friends or Foes?". after being rejected to come with her for Lunch, Sakura is talking to herself how they would be together as a squad for a long time so there's plenty of time to get to know Sasuke. Obviously this isn't the case as a bit after the Chunin Exams Sasuke left and joined Orochimaru.
I am curious though how long Sasuke was actually in the squad, just to see how woefully optimistic Sakura was.
This is what I managed to find, looking at the anime and manga and doing a little research on the internet. It is known that the day of the Ninja Graduation Ceremony is around January 22 (Naruto was still 12 years old), since the story began on January 18 and January 23 is Kiba's birthday (who graduated from 12 years), and because the registration was around 2 days after the start of Naruto's story.
Then we have the day when the fights with the Sound Four and the fight in the Valley of the End occurred, which is the official day of the end of team 7. That day is no later than September 22, it is between the 2 and September 22, on those dates all the events are fulfilled, including that Tsunade must be older than 50 years, that Shikamaru is 12 years old when he becomes Chunnin, among others. Let's meet the following.
-22 January - Team 7 formation
-22 September - Fight in the valley of the end
So Sasuke was about 8 months on the team. This is the closest answer.
Sources: Manga, Anime, Databook 1 and 2, Internet.
