My Diploma Engineering also took several months but my consultant told me it won't be any problem as long as it is compleated. Rest Seniors can put more light on this issue.
Total duration counted for a course to be completed will be its actual duration. If it has taken more time then the regular time then only regular time should be counted and treated and the status of the course should be completed. Hence it will be counted but only with the regular time taken to complete the course