How many gigabytes of files do you have? How many of those are compressed
or *.ZIP files (which take longer to scan)? Do you have the antivirus
program set to scan all file types or do you exclude those not known to
harbor viruses?
Currently I have about 40GB of files spread out on various drives. I use a
different program than you but as a measuring stick it takes about 2 hours
to do a full system scan. 29 hours seems like an extra long amount of time.
You may want to check with Symantec's tech support to find out if that is
normal for your configuration.