Taking too long to generate a ScreenShot in ffmpeg

I am generating a Screenshot by using ffmpeg. Its generating the thumbnail but its taking too long (more than 2 minutes).

I have referred this link

create thumbnails from big movies with FFmpeg takes too long

But I have to set in my nodejs code

ffmpeg(main_folder_path)
  .on('filenames', function(filenames) {
    console.log('Will generate ' + filenames.join(', '))
  })
  .on('end', function() {
    console.log('Screenshots taken');
  })
  .screenshots({
pro_root_path+'public/uploads/inspection/'+req.body.clientID+'/images/'
timestamps: [30.5, '20%', '01:10.123'],
filename: 'thumbnail-at-%s-seconds.png',
folder: pro_root_path+'public/uploads/inspection/'+req.body.clientID+'/images/',
size: '320x240'
  });

I used timestamp But even though its taking more than 2 minutes. How do I fix this Issue.