ya it was like that in the trimester system. we just didnt have the time to study for the comp. no idea why it takes extra 6 months in the new 2 semester model. But at other caribbean schools - people complete comp shelf within 18 months of starting basic sci - other wise I think they get dismissed if they dont pass it within a certain time (maximum 24 months). I personally took my comp shelf 2.5 months after basic sci and spent a month practicing more questions before taking step 1. I did well in basic sci (mainly cause I started off at AICASA BSEP which helped me have a handle on AUA). so the material was still fresh in my mind - just did qbanks. The pass mark for us was around 64 nbme comp shelf.