changing 404 or public access for future posts?

Hi all.

I am trying to set a custom message for future posts so instead of linking to a 404 page it says something like “This post isn’t live yet.”

I have modified my single post php file to have
If future then post “coming soon”
Otherwise post normal content

Which works fine….. until I log out of wordpress.
where I discovered that because I wasnt logged in it still directed me to a 404 error.

So the question I have is how can I either make future posts public but not appear on my home page until the scheduled date.
OR
stop the 404 redirect on future posts and change it to my own custom message.

Hope this makes sense.
Thanks in advance as always
-Tom