Macro time offset

I want to create a "fade out" macro that applies to the end of a clip. I can make the macro, but the timing of key-framing is only appropriate for a specific clip length. So 1: how do I delay/offset the timing of a effect or its key-frames, and 2: how do I get the length of the current clip?

For a 10 frame long effect I'd imagine it looking something like:
(get clip frame length) -> (subtract 10) -> (frame delay) -> (macro input + my effects) -> (output)