It is not the parade as you would vision. They will start early in the AM (mostly with extras as the crowd...they generally are there for the entire taping). The filming can take hours even days to complete. What they do is they will bring 1 float out at a time. They will film it coming down Main Street, then they will back it up and do it again and again until they feel they have the shoots that they want. That float will then leave and about 5-10 minutes later the next float will come out and they will do the same thing with that float. It is not the complete parade in one shot, it is a very long and drawn out process for that perfect shot. You might want to plan just to watch a little bit of it (one float maybe) but don't plan your whole day around it...it get's very tideous and can be boring if you have little ones.
The parade that they will be running at 3pm (maybe...last year it was pushed back until 5pm due to filming) will be Share a Dream Come True, the regular day parade for MK.