The default display mode for time periods is in hours. Other possible modes are 8-hour days and 24-hour days. The value 48 hours will show up as 6 days if 8-hour days is selected and as 2 days if 24 hour days is selected. To change the general visual display of time periods:
in the preferences dialog, in the tree, expand the Time/Date display item and select the Hours/Days display item
in the right hand side panel, select your mode.
Note that this will change the setting in all columns, tooltips and reports. You can override this setting for a specific column as described here.