Hello,
Right now there is not a way to force the import process for a site within the interface of SmarterStats. There is one work around that I can think of though. If you go into the site settings as a system administrator and just click 'Save' without making any changes, all tasks for the site are reassigned which includes the process of log importing. Do keep in mind this might not be instant though as there may be other tasks assigned to other sites that might be in queue before the site that your working with.
Hope this helps.