You might get the error below when trying to insert a Timeline filter in an Excel Pivot table that is built off of an SSAS (SQL Server Analysis Services) Cube. Timeline filter is a new feature of Excel 2013 that can be used as a ‘visual filter’ to filter data in pivot tables.
We can’t create a Timeline for this report because it doesn't have a field formatted as Date.
It appears that the Timeline filter requires the MemberValue property of the key column in the date dimension to be a date field (date or datetime both works). So to resolve this issue, just point the ValueColumn property of the key column of your date dimension to a date field as shown in the screen shot below.
Also, please note that Timeline filter also requires the Type property of the date dimension to be set to Time. Hope this is helpful.