It is in total about 6 hours. Mainly it's an interview about your past, relationship with your parents, childhood etc. Some intelligence tests but they are not very stressful (apart from the normal interview stress). Intelligence tests will test you on short term memory, association abilities etc. You do not have to ace the tests. It will end with a questionnaire containing about 360 statements wich you will answer if they are true regarding to you or not in order for them to create a personal profile. You will not have to do tests of your capacity to do several things at the same time.