Allow the definition of a standard day

Our standard day is 7.5 hours.  But some of our employees work 5 days and some work 5.5 days.  for those working 5 days the system correctly shows a day as 7.5 days and therefore their reported hours and days both work.  But for those working 5.5 days the system calculates that their average day is 6.875 hours and reports their days of leave based on that figure which is incorrect.  I would like to be able to say a standard day is 7.5 hours for everyone.

Note that the system still handles leave correctly but when it reports the outstanding leave days it is slightly off.  If we report in hours it is correct but most employees want to be able to work in days.