Clock in, recording the current time moment in the timelog.
With a numeric prefix ARG, record the fact that today has only that
many hours in it to be worked. If ARG is a non-numeric prefix argument
(non-nil, but not a number), 0 is assumed (working on a holiday or
weekend). *If not called interactively, ARG should be the number of
_seconds_ worked today*. This feature only has effect the first time
this function is called within a day.
PROJECT is the project being clocked into. If PROJECT is nil, and
FIND-PROJECT is non-nil -- or the user calls `timeclock-in'
interactively -- call the function `timeclock-get-project-function' to
discover the name of the project.
(fn &optional ARG PROJECT FIND-PROJECT)