From V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016) :
TTFN
Ta-Ta For Now (slang, Usenet, IRC)
From The Free On-line Dictionary of Computing (30 December 2018) :
TTFN
ta-ta for now - goodbye for now. Used in the UK, USA
and probably elsewhere.
(1998-07-02)