Check chapter 17 of the Admin Guide. The accounting logs under PBS_HOME/server_priv/accounting/ should have the information you need. Generally, you’ll want to write custom scripts to extract and summarize the data for your particular needs. Google for parse PBS accounting logs finds a few open source PBS accounting log parsers you could use as examples. I have no experience with them–we wrote our own.
The quick easy way is to write a bash script and parse the output of qstat at the end of each day. A longer term solution is to write your own python or perl script to parse the logs.