According to the links below from the SANE project, my Genius Colorpage HR8 scanner is not supported by neither the stable release nor the CVS version of the SANE Genesys backend.
http://www.sane-project.org/unsuppor...rpage-hr8.html
http://www.sane-project.org/lists/sa...html#S-GENESYS

Is there a way to get it working under Linux? If not, does it take a long time for the SANE devlopers to come up with a driver for the GL841 chipset which the scanner is based on?

If there's no support listed, then I doubt that you'll be able to get it working, unless by some miracle you can find a working driver that the Sane project doesn't know about. And it's anyone's guess when they'll have support for it. It could be next week, it could be never. It all depends on how difficult the scanner commands are to reverse engineer and how much interest there is in working on this particular scanner. I waited 3 years myself for a driver to be written for a Canon scanner I had, but it still isn't supported even now, since Canon refuses to document their interfaces. Unless you're prepared to wait and hope, your best bet is probably to do what I did and dump the one you have and get something you know is supported.

(Note: the preceding was just my opinion. If someone else knows better, I hope they'll chime in here.)