Under current policy, Thompson Reuters (the owners of ISI Web of Science) do not calculate Impact Factors for ANY proceedings titles. Therefore, proceedings journals are not issued with Impact Factors.
The ISI Web of Science platform itself is split into two components: SCI (the Science Citation Index) and CPCI (Conference Proceedings Citation Index). Proceedings journals appear within the CPCI. In order to access both users need to have a full subscription to ISI Web of Science. However, those subscribing only to the SCI component will not have access to proceedings papers.
However, it is at the discretion of Thomson Reuters, the owners of ISI Web of Science, as to how quickly they process and upload new content. Unfortunately, we have no control over how long it takes for each volume to be indexed. It can often take some time for papers to appear.