what is "I won' t be a jiffy."?

Question

what is   "I won' t be a jiffy."?

Answer

http://en.wikipedia.org/wiki/Jiffy_(time)

Jiffy is an informal term for any unspecified short period of time, as in "I'll be back in a jiffy".
I won' t be a jiffy. = I won' t be late

Answer

I won' t be a jiffy. = I won't be a second.
In other words, I'll be quicker than that.

http://www.thefreedictionary.com/jiffy

Answer

is it, "I won't be but a jiffy?"

I won't take a long time.  I'll be done very quickly, etc.

jiffy = slang for short period of time / quick

Answer

sounds very unnatural. is it from a textbook?