I have data in my sheet like the following:
Day Area AVG(Time)
-----------------------------
2013-07-01 LINE1 49.703432
2013-07-02 LINE1 38.
Select ColumnsA:C, Insert > Tables - PivotTable, Pivot Chart and choose New Worksheet or Existing Worksheet to suit. Drag Day
to Axis Fields (Categories), Area
to Legend Fields (Series) and AVG(Time)
to Σ Values. If required, left click on the contents of Σ Values and select Value Field Settings... and Sum.
Right click the chart (presumably a pie) and select chart of choice via Change Chart Type...
To remove references to (blank)
restrict you input to the PT by clicking on the PT and PivotTable Tools > Options > Data, Change Data Source.