Final answer:
The specific time required to tread water for the Swim School blue stage safety benchmark is not given; check the swim school's guidelines for exact requirements.
Step-by-step explanation:
The length of time a student must tread water to complete the Swim School blue stage safety benchmark is not provided in the information given. Swimming benchmarks usually consist of specific skills and times set by individual swim schools or organizations. To determine the specific requirements for the blue stage safety benchmark, it is best to consult the guidelines established by the particular swim school or program. Typically, students are required to tread water to demonstrate their ability to stay afloat and maintain control in the water as part of their swimming proficiency and safety training.