Try the FULLSTIMER and STIMER options. Good chance what they report is OS dependant.
The following is from the online manual:
Interpreting FULLSTIMER and STIMER Statistics
Several types of resource usage statistics are reported by the STIMER and FULLSTIMER options, including real time (elapsed time) and CPU time. Real time represents the clock time it took to execute a job or step; it is heavily dependent on the capacity of the system and the current load. As more users share a particular resource, less of that resource is available to you. CPU time represents the actual processing time required by the CPU to execute the job, exclusive of capacity and load factors. If you must wait longer for a resource, your CPU time will not increase, but your real time will increase. It is not advisable to use real time as the only criterion for the efficiency of your program because you cannot always control the capacity and load demands on your system. A more accurate assessment of system performance is CPU time, which decreases more predictably as you modify your program to become more efficient.
The statistics reported by FULLSTIMER relate to the three critical computer resources: I/O, memory, and CPU time. Under many circumstances, reducing the use of any of these three resources usually results in better throughput of a particular job and a reduction of real time used. However, there are exceptions, as described in the following sections.