Automatic CreatedAt and UpdatedAt with onModelCreating and a generic BaseEntity

Question

I am trying to implement something like this accepted answer but my BaseEntity is a generic class which looks like this:

public abstract class BaseEntity<TKey>
{
    public TKey Id { get; set; }
    public DateTime CreatedAt { get; set; }
    public DateTime UpdatedAt { get; set; }
}

Now I want to implement Timestamp addition on the SaveChangesAsync() method, but I have no idea how to go about doing that. My code looks like this:

... 
var entries = ChangeTracker
            .Entries()
            .Where(e => e.Entity is BaseEntity && (
                    e.State == EntityState.Added
                    || e.State == EntityState.Modified));

foreach (var entityEntry in entries)
{
   ((BaseEntity)entityEntry.Entity).UpdatedAt = DateTime.Now;

   if (entityEntry.State == EntityState.Added)
   {
         ((BaseEntity)entityEntry.Entity).CreatedAt = DateTime.Now;
   }
}

but the issue is BaseEntity is a generic type so the comparison doesn't work.