Hi Andy,
Welcome to the community!
The default build time limit for sites is 15 minutes and your build is exceeding that as you were able to see in the deploy logs:
5:27:38 PM: Execution timed out after 18m0.361315378s
I’d suggest taking a peek at this forums article on optimizing your build time: [Support Guide] How can I optimize my Netlify build time?
Fool wrote it so it’s pretty good! See if you can apply any of his advice.
If that doesn’t work, we can increase the build time limit for the site but please keep in mind that a starter account includes 300 build minutes, after which you will begin to accrue additional charges (see our billing FAQ for additional details on how we bill for metered services.)
If you’d like us to increase the time limit, let us know what you think a good value might be. 20 minutes? 30? Let us know.
Elden