You may try this:
$date = Auth::user()->created_at;
\Carbon\Carbon::createFromFormat('d/m/Y', $date)->diffForHumans();
Also you may try this (if you want to use createFromTimeStamp
method):
$date = str_replace('/', '-', Auth::user()->created_at);
\Carbon\Carbon::createFromTimeStamp(strtotime($date))->diffForHumans();