Scheduling Time for a Active Directory User

Question

Hi guys I am doin one of my project in User Application Management.
Actually i have to give Certain Amount of time for a Active Directory User  to Access a particular Application.
Is ther is any way to set time for the Users in Active Directory [Hopefully C# Coding would be most helpful]
Also i need to Alert the user at some time before his time end...
Is These things Possible???
I have a little ideas over running scripts only....rest all i m blank
Could any one Help me?