Returns the current run time for a process.
mp
process-run-time process => time
| process⇩ | 
A process. | 
| time | 
A positive integer or  nil. | 
The function process-run-time returns the current run time for process in internal time units. If the value cannot be determined (currently this is only on FreeBSD), then the return value is nil.
The value returned by get-internal-run-time is similar, but on some operating systems it is the total time for all Lisp processes in the image.
LispWorks® User Guide and Reference Manual - 01 Dec 2021 19:30:51