Get running time of child process

[Franco Martelli]

Hi,
Get running time of child process
I've Picom running on my system with these PIDs:
~$ pstree -hpan | grep picom
  |   |   |   |   `-grep,6199 picom
  |-picom,1620 -b --config /home/myuser/.config/picom.conf
  |   `-{picom},3507

If I do:

~$ ps -eo pid,lstart,etime | grep 1620
   1620 Mon Nov 20 16:12:47 2023    01:22:39

1620 is the PID of the parent process, the command returns the date when 
the parent process had started and the elapsed time as I expected. But 
if I do the same command for the its child process (PID 3507):

~$ ps -eo pid,lstart,etime | grep 3507

the command returns nothing.
So, is it possible to have the starting time and the elapsed time of a 
child process?
Thanks in advance, kind regards
--
Franco Martelli