Did a little research on how long parades in the past decade ran from start to finish. While Magic Happens is my current favorite out of all these daytime parades, it runs significantly shorter than a few that ran before. It still does an AMAZING job at standing out from its predecessors and is a new, fun, one of a kind experience! If it ends up running anywhere near as long as soundsational (my guess is 3-5 years) They probably have room to add a few more floats if they wanted to.
Here are the Run times for the last several parades we've had. These times are based on start to finish from a viewers perspective, not from step off to the end of the parade route.
ACF: 22 minutes (longest)
Soundsational: 18 minutes
Paint the Night: 17 minutes
Frightfully Fun: (shortest) 10 minutes, 12 if you count the headless horseman
Pixar Play Parade (pixar fest version) 17 minutes
MSEP: 19 minutes
Parade of Dreams (50th Anniversary Parade) 16 minutes
And lastly, Magic Happens clocks in at around 12 to 14 minutes