Call to a member function diffForHumans() on string in laravel 5.4

In my laravel model i am using

getTimeagoAttribute()

in this function i am try to get that timeago value for example when i post one review at 11.30 and now the time is 12:30 means i want to display 1 hour ago near the review and code inside my function is

public function getTimeagoAttribute()
    {
        $mytime = \Carbon\Carbon::now();
        $date = $mytime->toDateTimeString()->diffForHumans();
        return $date;
    }

When i try to run the code its show me an error Call to a member function diffForHumans() on string is this correct way to achieve what i want or is there any other method to acheive this..

This is how i achieve in my blade view

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please help me out to achieve this ..

via Chebli Mohamed