When to switch contact-lens case when cleaning every two weeks?

After two years of successfully wearing Ciba O2 Optix on a six-day,
five-night schedule before disposal
(<URL:http://groups.google.com/group/sci.med.vision/msg/e9347849f7843096>),
I've recently switched to Acuvue Oasys on a six-day, five-night
schedule each week for two weeks before disposal. That means I have to
start cleaning lenses again.

I know it is a good idea to regularly switch to a new contact-lens
case every [month|two months|three months, depending on the source of
the recommendation], but I presume this is for daily-wear users who
clean every night. I only use a case for cleaning once every two
weeks. I never reuse solution and always rinse out the case and lids
with hot water before letting them air dry. In my situation, how long
can I safely use a case before it's a good idea safetywise to switch
to a new one?