If the estimated time to completion keeps rising for a drive during the wiping process, one of two things may be the cause. One scenario is that the drive being wiped is finding too many dirty sectors and has gone bad, this can be verified by a rising number of dirty sectors being displayed next to the drive's progress bar. Unfortunately there is nothing we can do and you will need to replace the drive as it is no longer functioning properly.
The other scenario is that the drive's writing cache has been filled with data and the writing performance that the cache offered the drive is no longer in effect. This is generally verified by a lower data transfer rate, which can be seen in the drive's progress bar. Unfortunately there is still nothing that can be done to resolve this as it is resulting directly from the hardware limitations.