I am trying to use calculations with time in the form hh:mm - hh:mm and EXCEL
does not like negative time. The calculation is to accumulat over a week the
actual time worked by aggregating the hours worked on a daily basis. Thus at
the end of the week the time worked is ((monday time worked) XX:XX - 7:12 +
(tuesday time worked) XX:XX - 7:12, etc for the week)