As a guard 2ic in the past, i do allow my sentries to seat down
during their duty if its in the wee hours of the morning from
midnight-4am as few people come into camp at those times but the
4-6 shift will normally be made to stand after 5 as people start to
come in. However SBO and rifle must always be on and never taken
off.
Sometimes i just go accompany by sentry standing if i'm bored and
want someone to talk to so on those time he stands because i stand
with him.
PES C will also do guard duty. Only PES unfit will do duty
clerk/storeman etc but that depends on the different units i think.
For all PES fit personnel, as long as you cleared your range, you
can carry arms and either do prowler or sentry. For those who
didn't go through range or excuse firearms for some reason, you'll
only be allowed to do prowling using batton and shield.