I know how to thumb the spool and all. But my problem with bait caster is when to release my thumb off the spool during the cast. People say I begin the cast to early ( when the plug is above my head).

     I basically would like to know is when to release the plug during the cast.

I release the spool when I flick my wrist then casting.

Flick wrist - release spool.

Give it a try.  

    Go with what Sam said, that is exactly what I do.

That's a hard one man! It's almost second nature to me now so i don't even think about it.

Picture a clock where 12 o'clock is above you. 9 o'clock is directly in front of you and 3 o'clock behind you. The approximate release point is usually somewhere between 12 and 1 o'clock for an over hand cast, maybe around 12:30.

if your backlash is at the start of the cast you need more centrifugal or magnetic brake.if it's during the middle of the cast you need more thumb or spool tension.