Nova - update user_verified_at

Hello all -

So I want to have a boolean option in the edit user view within Nova.

But if the admin switch true or false, I want to pass timestamp (for true) or Null (for false)... I'm triping up somewhere

Heres my code;

        Boolean::make('Verified?', 'email_verified_at')
            ->trueValue(function(){
                return date(DATE_ATOM, mktime(0, 0, 0, 7, 1, 2000));
            })
            ->falseValue(Null),

Error is:

Preg match expects param 2 to be a string

Cheers - Ant