The editing of the movie left me a bit confused as to the passing of time on the ship. How long did Rose and Jack know each other? From the scene where Jack first notices Rose to the ending of the film.
Read the movie timeline. The relevant sections are:
Friday 12th April: Titanic sets sail from Southampton; that night, steerage passenger Jack Dawson meets First Class passenger Rose Dewitt Bukater.
Saturday 13th April: Jack Dawson dines with Rose Dewitt Bukater.
Sunday 14th April: Titanic hits the iceberg.
Monday 15th April: Titanic sinks.
So three days.