Execute the following Microsoft SQL Server T-SQL script in Management Studio Query Editor for finding the last modified date for all stored procedures.
 
-- SQL stored procedure last modified date - SQL datetime to string conversion
USE AdventureWorks2008;
 
SELECT   SchemaName = Schema_name(schema_id),
         SprocName = name,
         CreateDate = left(convert(varchar,create_date, 120),10),
         ModifyDate = left(convert(varchar,modify_date, 120),10)
FROM     sys.objects
WHERE    TYPE = 'P'
         AND is_ms_shipped = 0
ORDER BY SchemaName,
         SprocName
GO
/* Partial results
 
SchemaName        SprocName                     CreateDate  ModifyDate
HumanResources    uspUpdateEmployeeHireInfo     2016-01-11  2016-03-10
HumanResources    uspUpdateEmployeeLogin        2016-01-12  2016-02-16
HumanResources    uspUpdateEmployeePersonalInfo 2016-01-17  2016-06-12

*/