You do it before while you're still in the air. You don't lose almost no altitude between the J.c and 214b if done correctly
Also found a pretty devastating corner combo that works on everyone except Tager and Carl.
It does about 7053 dmg.
7 Stars
J.c-> 5c-> 623a~a-> Air Throw-> 'falling' J.c-> 236a (very tight timing)-> 5c-> 623a~a-> Air Throw-> 'falling' J.c-> 214b midair-> J.c