The group exercises are int he morning then the interviews are after lunch. There were only two pairs of interviewers (well there were at my S3) and each interview lasts an hour so there can be quite a bit of waiting around for those who are last. I was last and i think i finished around 1700 but if your first you could be finished by 1400. Dont hold me to these this is just to give you an idea from my experience at S3
Hope this helps
This was in july and held in Bmth dont know if it is still the same