I just added a new feature related to par-check - the option "ParTimeLimit". It's pupose is to cancel par-repair if estimated repair time is too big. It's not that important on a normal x86 computers. But on NAS with very slow CPUs the repairing can take very long time if many blocks are damaged. For example, one of my last downloads took 13 hours for repairing. In such cases it is often better to stop repairing, copy files to pc and repair there.
Unfortunately libpar2 doesn't have a built-in ability to cancel the process. I was needed to write a little patch. The patch is included in nzbget's distribution. I also submitted it to libpar2 developers. But the development of libpar2 seems to be stopped for more than two years; I don't expect the patch to be applied to the official libpar2 distrubution any soon.
Anyway I patched libpar2 in optware, so the optware users of nzbget will benefit of the new feature without any possible inconveniences with recompilation of libpar2.
Implemented in revision 249 (subversion) and will be also available in the next testing version.