It is hard to pin down the dates of the events of the Karate Kid before the Halloween dance. The only clue we get is at the begining of the movie which opens with Newark, New Jersey September.
However, I believe we can safely say the arrival in Receda was on Saturday, September 10th. Here is how I came to that conclusion.
We know that Mrs. Larusso is doing all the driving which means they are not going to make it too fast across the country. They are going to have to take plenty of rest stops and lunch breaks plus we can see from the opening few shots that they seem to be taking the scenic route. I figure it would take them 6 or 7 days to drive cross country, more likely 7 days espcially in that beat up 1968 Chevy Malibu wagon.
We also have to keep in mind the day they arrive Daniel meets Freddy Fernandez and is invited to the "Adios a Summer" beach party. The next day is the beach party and Daniel's violent introduction to Johnny Lawrence. Then the next day after that school begins.
At least back in the old days it was tradition for public schools to start the school year the week after Labor Day. In 1983 Labor Day was on Monday September 5th.
Had they left New Jersey on the 1st of September, the earliest possible given the information provided at the beginning of the film, that would put them in CA on the 8th which was a Thursday putting the first day of school on a Saturday. Of course that's wrong.
So assuming West Valley High School followed tradition and started school the week after Labor Day the timeframe fits that the Larusso's left New Jersey on the 3rd of September, traveled 7 days cross-country, arrived in Receda on the 10th, the beach party was on the 11th, and the first day of school was on the 12th.
This is just a theory however based on the assumption that Daniel's new school followed tradition. I wouldn't have any reason to believe that they wouldn't so I do feel confident in my timeline.
