Green’s Dictionary of Slang

t.t.f.n. phr.

[ta-ta for now, orig. created and popularized on comedian Tommy Handley’s BBC Radio show ITMA (It’s That Man Again, 1939–49). Dorothy Summers, as ‘Mrs Mopp’ (the comic charlady) actually used the phr., which was revived by BBC Radio 2 disc jockey Jimmy Young (b.1923)]

goodbye.

1944
195019601970198019902000
2003
[UK]A. Morrison letter 22 Feb. in Morrison Things My Mother Never Told Me (2002) 93: TTFN. DILY. DDYLM.
[US]Eble Campus Sl. Apr. 10: t.t.f.n. – good bye.
[NZ] McGill Reed Dict. of N.Z. Sl.