[Leica] Utility to batch correct date/time of Raw files?

[Peter Klein]

On my recent trip to Spain, I neglected to change the date and time on 
my camera's clock.  So all the EXIF data is nine hours earlier than it 
should be. Is there a reliable utility that can batch-edit the EXIF data 
in the Olympus Raw files (.ORF) and correct them to when they oughta 
be?   I want to be able to tell the program, "Take all files in this 
folder and advance the time in the EXIF by 9 hours, so both the date and 
time will be correct.

I have FastStone Image viewer on my PC.  It appears to have this 
feature.  Has anyone used it? Is it reliable?

Other suggestions happily considered as well.

Thanks!
--Peter