The MDX function SchemaRefreshTime gives you this information. So you can use a "Simple Table" widget with a "Plain MDX" request:
with
member [Measures].[Schema Refresh Time] as SchemaRefreshTime(),
FORMAT_STRING = "j:HH'h'mm"
select [Measures].[Schema Refresh Time] on 0 from [Sales]
The FORMAT_STRING is using a Java simple date format.