In our shop we have a software(Cycle View) which gives elapsed time of a job. I think other than this what i know of is one would have to scan the SAR and look for string "** EOJ" and in same line ELAPSED TIME=.
You may want to search in DFSORT forum and i think sometime back i saw a posting using DFSORT to extract SAR records.
which will create you a dataset with SAR information. Dataset will be Recfm VBM, Lrecl 137.
Or in your shop there must be production datasets with sar information
find that out and then you can write a SORT step to extract **EOJ line where job name is job you want to extract. Assuming you want to do this for job runs over period of time. This way you can concatenation multiple files.