O comando ps
pode mostrar a hora de início ou o tempo decorrido:
$ ps -O start,lstart,etime
PID STARTED STARTED ELAPSED S TTY TIME COMMAND
7827 15:18:42 Tue Aug 1 15:18:42 2017 00:00 R pts/12 00:00:00 ps -O
10413 Jul 16 Sun Jul 16 17:36:12 2017 15-21:42:30 S pts/12 00:00:07 bash