In PowerShell:
Without -p option: 0.76elapsed
time rshell --quiet 'exit'
0.00user 0.00system 0:00.76elapsed 0%CPU (0avgtext+0avgdata 5140maxresident)k
0inputs+0outputs (1338major+0minor)pagefaults 0swaps
With -p option: 1.77elapsed
time rshell --quiet -p COM6 'exit'
0.00user 0.00system 0:01.77elapsed 0%CPU (0avgtext+0avgdata 5128maxresident)k
0inputs+0outputs (1336major+0minor)pagefaults 0swaps