Prevent more user from edit in same record

Question

suppose i need to make update the employee as following  
CREATE PROC UPDATE_EMPLOYEE
(
@EmployeeID INT,
@EmployeeName NVARCHAR(50)
)
AS
update Employee set EmployeeName=@EmployeeName where EmployeeID=@EmployeeID
Suppose I have two useres A,B
A modified or edit using stored procedure above employee no 5000 field EmployeeName
B need to modify employee no 5000 using stored procedure above field EmployeeName
i need to prevent user B To modify same record using time stamp How to do that from c# code and sql server and what modification in stored procedure to accept timestamp
EmployeeTable
EmployeeID
EmployeeName
TimeStampEmp
Meaning allow to another user after specified time