A reader for the timeclock file format generated by timeclock.el (http://www.emacswiki.org/emacs/TimeClock). Example:

i 2007/03/10 12:26:00 hledger
o 2007/03/10 17:26:02

From timeclock.el 2.6:

A timeclock contains data in the form of a single entry per line.
Each entry has the form:

  CODE YYYYMMDD HH:MM:SS [COMMENT]

CODE is one of: b, h, i, o or O.  COMMENT is optional when the code is
i, o or O.  The meanings of the codes are:

  b  Set the current time balance, or "time debt".  Useful when
     archiving old log data, when a debt must be carried forward.
     The COMMENT here is the number of seconds of debt.

  h  Set the required working time for the given day.  This must
     be the first entry for that day.  The COMMENT in this case is
     the number of hours in this workday.  Floating point amounts
     are allowed.

  i  Clock in.  The COMMENT in this case should be the name of the
     project worked on.

  o  Clock out.  COMMENT is unnecessary, but can be used to provide
     a description of how the period went, for example.

  O  Final clock out.  Whatever project was being worked on, it is
     now finished.  Useful for creating summary reports.