Building a web site always takes longer than expected. And the size of the web site does not seem to matter. There is an inverse relationship between cost and commitment: A $10,000 job with 100% commitment takes about the same time as a $1,000 job with only 1% commitment. And who can commit to any project 100%. The point of this is that that web site's "holding page" better be useful. An "under construction" sign does not help your client or your client's audience.
For example, the holding page at Social Venture Partners Rhode Island (svpri.org) is a one page web site. It tells you who they are, what they do, what is happening, and who to contact. All this on one page and maintained with an insignificant tool -- a few dozen line PHP script.