Exporting certain reports to XLSX may result in the exported document's cells being set to an incorrect format. This is a bug, resolved in 7.3 SP2.
The issue here is that the user’s date and time format is being applied to the majority of non-integer fields when exporting certain reports. This is most commonly seen on reports involving the Forecast table.
When CRM does an export, an intermediate XML file is created. An entry type property is applied to each cell data field in the XML file. These are the same as the Colp_EntryType values on Custom_Edits. This file is then used for generating the requested Excel document. Should these fields represent an integer, currency or datetime field, the appropriate field type is set in Excel, otherwise a Text type is used.
This functionality can be verified by right-clicking on a text field, then selecting the Format Cells option. In cases where this issue is happening, the majority of fields in the export will have a data type set to the user’s date format plus their time format. In the cell properties, the format will have a value like this:
dd/mm/yyyy hh:mm AM/PM
This is resolved in 7.3 SP2, due for release on the 22nd of April 2016.