Well the short answer would be yes, and yes, a site under construction can rank for search terms within search engines. But think very carefully before embarking on SEO work before a site is fully completed.

One reason why you should not invest too much time on such a site, would be that any changes to text and site structure will affect your rankings – you are best working on the site when it is fully completed.

Another reason – Directory Submissions for example, are always worth doing once a site is up and running to avoid multiple rejections from webmasters. You will also gain the benefit of a clearer understanding of your main keywords to be used within the site

Rather than attempt to complete the SEO work as quickly as possible, allow time for the site to grow naturally, steadily. Your time will be better off spent planning the SEO required for any given project, rather than trying to implement them straight away. Write articles, do your keyword research, scout out the competition, start a small blog in the meantime to add some content to the site. Have your work ready, and it will be easier to implement once the site is live.