Yes, your 2D should be released the moment you hit j.2C. From there, wait a second and tap j.C (NO MASHING OMFG@!#@)
Volante is trickier. You use it only in combos you started with something that prorates relatively well. (Probably 5B, 5C, 6D, clap, air CH volante, 2D, allecan, etc.)
The trick (not really a trick) is to hit them as low as you can with your Alle-can. After that it's just input consistency on your part.
Usually I go Allecan > volante input > 5C > Volante hits > allecan > j.B > j.C > clap > j.2C rep.
I've also seen allecan > 5C > j.B > clap/ j.2C > j.C > dj.B > clap, as follow ups to volante hits.
4D combos are ones I haven't really gotten into yet.
Soujiro, It seems like if I try to input 4D with the same timing as volante in the allecan combo, it whiffs.
It'll look something like.. whatever > j.2C allecan > 4]D[C > j.C. My Jump B/C will hit, but the 4D won't.
How early should I be inputting the 4D?
Should it be j.2C 214C]D[ > 5C > j.B?