We do not stipulate the length of time the tasks should be, but approximately a minimum of 3 to 4 minutes per task is a suitable length to allow candidates to demonstrate their skills. Each task should not exceed 7-10 minutes.
A recommendation would be:
Task 1 (individual) – 3-4 minutes
Task 2 (paired) – 6-7 minutes
Task 3 (group) – 9-10 minutes