Sorry no solution for you but there is a thread on the mailing list which could be related:

http://minnie.tuhs.org/pipermail/ozt...il/012351.html

Peter has two TiVo's losing time - around the same amount too. I understand that both of his run CacheCards (like yours). Could it be ... ?

Craig Curtin theorised that Peter's problem could be a software issue in this post:

http://minnie.tuhs.org/pipermail/ozt...il/012361.html

Perhaps see how it goes without the CacheCard drivers?