Array as session variable

Yes, PHP supports arrays as session variables. See this page for an example.

As for your second question: once you set the session variable, it will remain the same until you either change it or unset it. So if the 3rd page doesn't change the session variable, it will stay the same until the 2nd page changes it again.

Yes, you can put arrays in sessions, example:

$_SESSION['name_here'] = $your_array;

Now you can use the $_SESSION['name_here'] on any page you want but make sure that you put the session_start() line before using any session functions, so you code should look something like this:

 session_start();
 $_SESSION['name_here'] = $your_array;

Possible Example:

 session_start();
 $_SESSION['name_here'] = $_POST;

Now you can get field values on any page like this:

 echo $_SESSION['name_here']['field_name'];

As for the second part of your question, the session variables remain there unless you assign different array data:

 $_SESSION['name_here'] = $your_array;

Session life time is set into php.ini file.

More Info Here