Question about Executive system ($ cmd) command

I’m study with website screenshot these days. I selected webscreencapture. I write the official bat command into php code. I have copied three webscreencapture.exe, I would like to catch 3 websites’ screenshot at the same time.

$cmd1 = 'webscreencapture1.exe  "" e:\\www\	est\\1.jpg';
$cmd2 = 'webscreencapture2.exe  "" e:\\www\	est\\2.jpg';
$cmd3 = 'webscreencapture3.exe  "" e:\\www\	est\\3.jpg';

Now I met a few problems.

  1. How to make PHP run $ cmd1, $ cmd2, $ cmd3 at the same time? Rather than the implementation of the queue?
  2. webscreencapture sometimes have bugs that has success get the page’s screenshot, but also repeated the system ($ cmd) command many times. How to do the one command only once, then automatic termination this line system ($ cmd) command?
  3. I did not find the time delay code from webscreencapture official website , I would like to catch some of the online video sites. How to set a time delay in the system ($ cmd) ?
  4. Is it possible to set the code that every 24 hours run the screenshot code automatically ?
    Thank you.

Up, How to make PHP run $ cmd1, $ cmd2, $ cmd3 at the same time?