You can estimate the practice tests times at about ten minutes per section for the younger grades, up to 15 minutes per section for the upper grades. You can find exact times for each grade's practice testing in the practice test teacher directions for that grade.
The purpose of the practice tests are to help give students an example of the format and procedures of standardized testing. The content of the questions and scoring are irrelevant. They can be sent home after completion, or thrown away.