\version "2.18.2"

% Thanks to David Kastrup for the inspiration!
after =
#(define-music-function (parser location t e m) (ly:duration? ly:music? ly:music?)
   #{
     \context Bottom <<
       #m
       { \skip $t <> -\tweak extra-spacing-width #empty-interval $e }
     >>
   #})

{ \after 4 \< \after 2 \> \after 2. \! c'1 }