It needs pretty much a full charge. Only useful when your fairly high up or still have a second jump.
Yoshi's fastest in the air, followed by Jiggly. I know that off the top of my head ^^; Dedede's the slowest in the air. Which makes me sad :x At least he climbs vertically and fast falls fast ^^;
Wario and Marth are really close, almost negligible, but Marth is faster. Wario also has better maneuverability in addition to speed. His aerial movement is just insane for a fat ass >.>
My Creations in Modnation Racers! Check zhem!
http://community.modnation.com/en-us/players/IvoYaridovich/creations