time [command] retorna o tempo gasto para o comando ser concluído.
steven@wind:~$ time du /storage -s
du: cannot read directory '/storage/lost+found': Permission denied
1548584024 /storage
real 0m4.046s
user 0m0.224s
sys 0m1.496s
steven@wind:~$ time sleep 5
real 0m5.003s
user 0m0.000s
sys 0m0.000s
steven@wind:~$