Sorry for my belated response, but I'm not sure I can answer your question.
AISI, there are different degrees of "bad". I would consider a sector to be uncorrectable, and therefore truly bad, if it could not be read, irrespective of the number of retries. Marginal or "weak" sectors may require several retries. Each retry would entail an additional rotation of the platters. This amounts to 8.33ms for a 7200 RPM drive. Therefore I would think that a sector that was recovered after 500ms should still be considered to be bad, depending on the context. However, it probably won't show up in the SMART stats.
CHKDSK records bad sectors in the $BADCLUS metafile. Even if the drive subsequently reallocates this sector, the $BADCLUS entry remains. It will be cleared the next time the drive is formatted.
Some sectors may come good under different environmental conditions, for example at lower temperatures. It could also be that the drive was being subjected to vibration when the data were being written, in which case the sector would come good when the data are overwritten. A "pending" sector is always retested before being considered for reallocation.
As silly as it seems, a common problem with difficult sectors is that the drive may hang, requiring a power cycle. ISTM that a drive should be able to seemlessly handle bad sectors, but this doesn't always appear to be the case.
See the [woeful] HD Tune performance graphs in this thread:
http://forums.seagate.com/t5/Barracuda-XT-Barracuda-and/ST31000528AS-CC37-drives-one-seems-fine-the-...Compare them against the results at the following page:
http://www.hdtune.com/testresults.html
