$ date -d "Sun Mar 3 18:05:17 UTC 2013"
Sun Mar 3 10:05:17 PST 2013
The above converts to the system TZ. Or:
$ echo $( export TZ=CST; date -d "Sun Mar 3 18:05:17 UTC 2013" )
Sun Mar 3 18:05:17 CST 2013
The above converts from any TZ to any other TZ, without resetting your shell's TZ variable.