laravel中的时间计算从用户输入

i want to calculate the time difference and insert it into database...my model name is "booking" and the start time and end time will be taken input from users..and total_duration will be calculated from these two and will be inserted into database...i use these codes...but won't working.this is my controller.

<?php
/*namespace App\booking;*/
use Carbon\Carbon;
namespace App\Http\Controllers;
use App\booking;
use Illuminate\Http\Request;
use Illuminate\Database\Eloquent\Model;

  class RoombookController extends Controller
  {
    public function showreport(Request $request)
     {
    /* dd($request->all());
     */  $time= Carbon.now();
        $booking = new booking;
       $booking->bookdate = $request->input('bookdate');
       $booking->roomname = $request->input('roomname');
       //echo $datefrom;
        $booking->starttime =$startTime= $request->input('starttime');
        $booking->endtime = $finishTime=$request->input('endtime');
        $booking->purpose = $request->input('Purpose');


    //echo $dateto;
    $time->sTime = Carbon::parse($startTime);
    $time->fTime = Carbon::parse($finishTime);
    $time->total_time = $fTime->diffForHumans($sTime);    
    $booking->total_duration = $time->total_time;

    $booking->save();

    }

}

Using Carbon for calculation execution time is not very good idea. Just use plain old microtime():

$start = microtime(true);
.... // Do something here.
$end = microtime(true);
$time = $end - $start;

I think you should first convert it into seconds

$totalDuration = $finishTime->diffInSeconds($startTime); 

and then desirable format

gmdate('H:i:s', $totalDuration);

or try this if this work for you

$finishTime->diff($startTime)->format('%H:%i:%s');