You're really looking of the modify_date in the
sys.objects table where the type is either a stored proc or a function. This works on a database by database level -- to elevate this search to the server level, you'll have to use the loop sproc
sp_msforeachdb
SELECT name, create_date, modify_date
FROM sys.objects
WHERE type = 'P' -- change 'P' to 'FN' if you're looking for a function
and modify_date between cast('2013-09-10' as date) and cast('2013-09-20' as date)