Just got back from our trip and we did have lunch at BOG. There was a line up, where they just asked if you had a FP...if you did, then they sent you to the check in line. Both lines moved very quickly. We actually got in the first line (where they don't actually check anything, just confirm that you have a FP) before our time, because it looked long. However, it moved so fast we had to get out to wait for our time! So I don't think you need to show up early.
I cannot stress enough that you should definitely pre-order. Once we checked in (which is outside the restaurant, at the beginning of the bridge) we were directed into the entrance of the castle/restaurant. There, a cast member asked for our name again, pulled up our reservation and scanned my magic band to pay for our pre-ordered meals. We were given a receipt and then went in to find a table (which was not a problem). Our food arrived within about 5 minutes of sitting down.
When we left, we saw a very, very long line of people waiting to order their food. I can't understand why people don't pre-order - especially since you can change your order. Pre-ordering will save you so much time, and should eliminate most line waiting!