Finish building a WordPress website, including some very basic integration with a third-party app

I have a website that's in development now - WordPress - and I need some help to finish building it out today so we can present to someone at the end of the day. The templates are created (though they will need some tweaking), the site map is done (about 40 pages in total, but most of them are just switching out copy), and the content (including text and graphics) is all ready to drop in place. Of course, there are a couple of issues that complicate things. First, the timing - that's the biggest challenge, of course. We don't just need someone who's capable on WordPress, we need a WordPress wizard to make sure things come together right the first time. Second, we want this website to link up with a third-party app on the back end. The way we would like it to work is that someone to login to the WordPress site we're building, and that login would be the same login that the person would use for the third party app. Once they've logged in to our our site, they will be able to click a button at certain points that would bring them to the third party app. Clicking that button would automatically bring them into that app without having to login on the app itself. We DO NOT have to do this fully and completely for this demonstration. If getting this job done means that we fake things by hard coding a couple of logins into the WordPress site so that those hard coded logins take you to the app and get you in, that would be fine. It just needs to show how things would work for the client. The site is already in development, so it would mean picking up from where it is now and moving on things with speed and precision. We would like the developer to be well compensated for the day's work and will make sure that you feel like you're getting value for your expertise.