About two weeks.

When / prerequisites:

1. Students do a thorough review of linear functions / formulas early in the semester, including computing the linear formula, making predictions, and interpreting the slope and intercept.
   
2. Students also learn to use spreadsheets for all of these computations and to graph non-linear formulas as well. This is included fairly early in the semester. 
   
3. The material on regression comes later, but when the students still remember the material about exact linear models and working with spreadsheets.