I am listed as having 14 hosts but actually only have 7. It happened when I reloaded windows on all of my machines. How long does it take for inactive hosts to disappear?

Here or in the projects?
Here you can simply delete them, or wait some time. Afaik they will disappear.

At the projects you can merge them on your computer page.

i think merging them manually at project's web site is the best option, but names of host should be the same (and sometimes there must be circle about month from last contact previous host with server)