When working with returning data from spreadsheets to reporting sometimes the formats specified in Excel for numbers and dates cannot be exactly matched into HTML to be displayed in output reports neatly.  When this occurs you can include your own rules on how an incoming excel format is to be presented back out in the report and this form is where you do that.

Copy the incoming excel format you want to change from the Raw Data form and then add this to the relevant tab Date or Number.  Then edit the To entry to give the desired HTML format (note remember in date format months are referred to in MM format and minutes in mm format).

Once you have your format as you want it this can be copied out as an XML definition and included in the standard sets of conversions to be used with this report (by including in the XSL for that report and then updating this to be shared centrally by other users), although you will need to be an admin user to do this.

For further detailed information about working with spreadsheets into reports have a look at the knowledge base article: http://www.projectinabox.org.uk/wiki/doku.php?id=3_3:kb0000390