You shouldn't need DataAnnotations as conventions will work for you in this case
Try the following
public class Time
{
[Key]
public int TimeId { get; set; }
public int EmployeeID { get; set; }
public int ProjectID { get; set; } //<< Changed type from string
public long? TimeSpent { get; set; }
public virtual Employee Employee { get; set; }
public virtual Project Project { get; set; }
}
public class Employee
{
[Key]
public int EmployeeId { get; set; }
public String FirstName { get; set; }
public String LastName { get; set; }
// Set up the other side of the relationship
public virtual ICollection<Time> Times { get; set; } // << Added
}
public class Project
{
[Key]
public int ProjectId { get; set; }
public String ProjectNumber { get; set; }
// Set up the other side of the relationship
public virtual ICollection<Time> Times { get; set; } // << Added
}
This article may help http://msdn.microsoft.com/en-gb/data/jj679962.aspx