How long does it take for the site to update?
The GitLab CI build itself takes about ~25 seconds to run. It is generally expected for your site to update around that duration, and take not more than a minute.
What environment is used to build and deploy the site?
From the .gitlab-ci.yml file, it can be seen that we use Docker image that comes with current Neuron and minimal shell environment. CI runs job named pages, which in turn calls neuron on checked out (master) working directory. It is set up to output built site to public folder, which is where CI expects it for deploying. For more info about how GitLab Pages work, see GitLab documentation.
Can I use my own domain name?
Yes, see section about Custom domains and SSL/TLS Certificates.