Duration of formatting depends on a few factors:

  1. type of format (full or quick)
  2. size of volume
  3. Speed, available RAM, host bus used, and system load of the host computer

A quick format takes less then 60 seconds, but a full format will vary according to the variables listed above. A full format on a 2TB disk can take overnight to format on a slow computer. If there is suspicion that the disk is not functioning correctly and the format is taking too long, you may examine Windows' system logs for fault, as described here: http://support.microsoft.com/kb/308427