Desired dwell times may vary depending on the type of memory, the age of the memory, the size of the unit of memory, operating temperatures, etc. Dwell times specific to a given embodiment may be gleaned from a lookup table which may be stored in memory. According to an illustrative example, which is in no way intended to limit the invention, a desired dwell time for a particular 19 nm multi-level cell (MLC) NAND flash memory may be 1678 sec (about 30 min) at a 40° C. operating temperature, which is equivalent to 260 sec (about 4.3 min) at a 55° C. testing temperature, or 13,076 sec (about 218 min) at room temperature (25° C.). Again, these dwell times are presented for a particular type of memory by way of example only, and are in no way intended to limit the invention. Preferably, the dwell time assigned to a given unit of memory is long enough to allow for any improvements in the unit of memory to occur. Thus, units of memory which do not have a particular dwell time associated therewith may be assigned a standard dwell time of about 4 hours, but could be longer or shorter depending on the desired embodiment.

The rate at which units of memory may be re-evaluated is typically slow, e.g., because the dwell time imposed on each unit of memory is preferably long enough to induce improvements therein. Moreover, the delay queue size is fixed. Thus, if additional units of memory are received to be re-evaluated while the delay queue is full, those additional units of memory may be automatically retired as previously mentioned. However, the low rate and implementation in the background desirably allows for minimal impact on normal operations.