Just a warning to other users, attempting to build a large index (ie thousands of posts) with Relevanssi will not work on a shared server, as you will most likely get a timeout:
Fatal error: Maximum execution time of 30 seconds exceeded in ...
The solution is not applicable if you are on a shared server, as you will not be given priviledges to alter the file, but if you can, you need to access the php.ini file (normally on root), find the line:
and change that to something higher than 30 seconds (ie 90).
Just thought I'd put that out there, seeing as I had this problem and couldn't figure it out for a while....
PS. This is not an issue with the plugin itself, but with your server setup and Apache.