If you have the copy and images and access to the domain, then a day for an experienced dev is doable, but only within an established relationship of communication and trust. Push back for time if needed, because a one-day turnaround does not allow time for their review and approval. Again, this would really only be possible in a high-trust, established relationship.
That said, here’s what I’d do:
Put the copy into Claude AI, ask it to generate a landing page using Tailwind. Build it locally and copy-paste the local output to statically linked files, push to GitHub, then host on Cloudflare Pages. If they need form submission, use Formspree free tier.
The design is clean and simple. Tell the LLM you want a space for a large image on the right and a headline, brief paragraph, and button CTA on the left.
If the landing page is for form submission, then put the headline and paragraph on the left, and the form on the right (on mobile, show the form first). The form needs a headline and a line of copy explaining why the user should submit (e.g., “Enter your details below to receive emails about this event” or whatever).
Under the form, a section with a contrasting background color to the top of the page with a headline, paragraph, and image about whatever the thing is.
Then another section that is just the form, centered.
Basic design advice: use more padding than you think! Make the headline big! Use a clean sans-serif font! Use white, dark dark grey, and a strong color like red for CTA. If you need color inspiration, use https://coolors.co to get nice, easy-on-the-eyes colors.
Be sure to include a footer, and ask the client to send you a privacy policy to include, also as a static page. That’s their responsibility, and tell them it’s not your area of expertise but they should be able to find information on a blanket privacy policy on Google. It’s not launch-critical, but letting them know about it before launch is better.
If they then want more pages, again, statically build them locally and push to GH. You can link them statically in the navigation. When they inevitably come and ask you for a blog and other things that a CMS like WordPress would be good for, tell them you can add that new functionality in a new project for $X.
Good luck!
(Also, everyday web dev does not need complex toolsets like the MERN stack. Basic PHP, SQL database, and whatever flavor of frontend framework is a lot easier to deploy and pass to everyday kind of clients, in my opinion.)
Edit: If I don’t feel like running a local build step just to get a compiled CSS file from Tailwind, I use https://play.tailwindcss.com/ to copy-paste HTML in and get the compiled CSS out. Saves time in some situations.