In the end it really doesn't matter.
I think though that it's wise not to schedule anything you think you might want to do with the rest of your life (in your case surgery) at either the very beginning or the very end of third year. There's a couple of reasons for this.
To be blunt, as a beginning third year student, you're really going to suck. You'll be slow, you won't know where to find things in the chart, you'll follow your interns around like a lost puppy. If you know that you want to do something, why suck when waiting a couple of months can make a huge difference, especially when third year clerkships are the time to plant the seeds of LOR's.
In terms of the end of the year, there's always the off chance that what you think you want to do, you'll actually end up hating. It would be really unfortunate if you spent all year thinking you wanted to do a surgical specialty only to find out that you generally hate the OR...after you've set up your M4 schedule, and when you may or may not have dismissed other specialties out of hand because you were focused on that last clerkship...
So play it safe, and put your interest in the middle. The rest of the schedule really doesn't matter.