HI,
It is not suggestible to change the time constraint of standard info type,
still if your client is looking for this,
then just change the info type 2011's time constraint from Z to 02 or 01,
if you make it 02- while saving the record with duplicate entries system will populate a warning message and will delete your duplicate entry.
if you make it 01 system will give you an error message while saving it self, if you are having any duplicate entry.
you can change the time constraint of the info types in V_T582A table.
Regards,
Prashanti Swain