You are given a 2 year period to complete the qualification, regardless of the level or size (Award, Certificate or Diploma). However, given that the qualifications are studied through distance learning, it is very much down to the amount of time you are able to devote to studying and completing the assignments.
Typically for a well organised student it takes around 3-4 months to complete an Award, 6-8 months to complete a Certificate and 12-14 months to complete a Diploma. However some have managed to complete much faster, while others have gone right up to their 2-year deadline.