I would avoid taking it at the beginning of the third year as you'll still be learning the ropes of the wards. I would also recommend avoiding scheduling medicine or ob-gyn right before the rotation as these are usually the other most time-intensive clerkships and you don't want to be exhausted before you even start. Additionally, if your school gives all the subject boards at the end of the third year or you plan to take step 2 relatively soon after the end of the third year, you might not want to take surgery as the last block. It can be hard to balance cumulative studying with studying for whatever clerkship you are on, particularly if it is one that you are aiming for honors in.