Variable: compilation--start-time
compilation--start-time is a buffer-local variable defined in
compile.el.gz.
Documentation
The time when the compilation started as returned by float-time.
Source Code
;; Defined in /usr/src/emacs/lisp/progmodes/compile.el.gz
(defvar-local compilation--start-time nil
"The time when the compilation started as returned by `float-time'.")