temp landing page but access rest of site

You could use a plugin like this one.

When you sign in as Admin you can access the website like normal, but everyone else will only see the under construction page.

OK create a new ‘page’ in your admin screen, then in the settings > reading, change the front page to a static page and select the page that you just created.

Hi. I did this for a website a moment ago.

Let’s say your landing page is landing.php and is placed at the root of your website.

Restore your default htacces (redirects to index, htacces don’t have to know your landing page)

Put this code at the top of landing.php:

<?php
session_start();
$_SESSION['splashscreen'] = true;
?>

Then in index.php of your current theme (before any html ouput):

<?php
session_start();
//	check if user have already see landing.php
if (!$_SESSION['splashscreen'])
{
	header("location: landing.php");
	exit();
}
?>

Now every time user will request a page from your wordpress blog, the server will check if a session variable called ‘splashscreen’ exists. If it doesn’t exists, (the first time) it will redirect the browser to landing.php and stop executing the script on index.php.
Then when passing through landing.php, the session ‘splashscreen’ will exist and equal true, so the redirection won’t happen and the landing page won’t show again until the user clears his browser’s session (force it by hand or quit the browser) and if you redirect from your landing page to another page of your blog, the code placed in index.php will execute as usual .

Sorry if instructions are messy and don’t make sense, don’t have enough time to explain now, but if it does not work, tell me and I’ll explain more.

Sorry not sure i understand what you want. Do you have an example?

You mean you wanna show the temp page between EVERY page click ?? Seriously? it would be very awkward, users will quickly get bored…

Did you try the first solution I gave you? I really think it would suit your needs.