Congrats to ixion for parsing it perfectly, but judging by the comments, maybe in retrospect my 11dn was too convoluted for its own good. Though answer comprises 2 straight-forward words, I had never heard of the expression before, and the Chambers' definition was unexpected. The definition is "bass organ marking" with "bass" as in type of fish; "beat" as in exhausted; "with finale" is "with final e"; all following a synonym for "later".
Hope that makes it a bit clearer.