I agree that you'll be able to see the tops of the floats and hear the music, but you won't have a very good view of anything that is on the street (there might be moments when the crowds part, but not for any sustained period). There is also the chance that they won't let you wait/request a patio table (most times I've been able to request indoor or outdoor, but there have been a few times when the CM said they were not able to accommodate requests). I think it's a fun way to see the parade, if you've already seen it from a better spot, but it's not a spot to watch from if it's the only time you'll see the parade.
In terms of timing, Carnation Cafe is a pretty quick meal. I'd say most guests take between 45 and 60 minutes for a two or three course meal. They're really fast to bring out the food. So if you really wanted to see the parade, I agree, a slightly later time would probably be better (~5:30 pm).