Category Axis fixed as days. Need to use hours & mins as well

I need to graph body temperature over time. The temp is measured from 1 to 4 times per day. The graph will collect values for between a week and about 6 weeks. The data table looks like the sample below, and the underlying Date-Time is a numeric time stamp.

Temp DateTime
37.2 10-Jul-12 23:47 A
37.7 11-Jul-12 06:15 B
37.5 11-Jul-12 19:18 C

On my graph if there are multiple measurements in one day they stack vertically instead of spreading over the day. Using the three samples above I currently get Point A over the X axis marker for July 10, and B & C directly over July 11. I would like B to display at an appropriate distance between the two.

I'm using a plain line graph. If I hover over the data points it the tool-tip shows the correct value, (including hh:mm)

I've tried changing the x axis scale but the minimum base unit is Days.

Any suggestions as to how I can fix it would be much appreciated! My 'in progress' spreadsheet is attached.
Temperature.xls

Use a xy-scatter rather than a Line chart.