Hi Umesh,
This is how standard SAP designed. If you look at the transaction VL10A under user role, you can see the profiles, under these profiles, you will define the number of days.
Now, as suggested by Glaucia, you can change the number of days in VL10CUC, but, i would suggest to create new one and give the number of days as 90 days. Now, you can ask whichever user wants to have 3 months to logon and change the default one to new one. This way you can avoid if same being used by other countries for them if the requirment is 30 days.
Note: I am not sure whether user can change or it has to be done by consultant, will check and get back to you.
Regards, Sai Krishna.