you need something like this:
?_do_confirm=Yes&_do_actions=yes&_transid=-1&view_name=hoststatus&site=&_ack_sticky=on&_ack_otify=off&output_format=JSON&_username=&_secret=&_down_comment=$YOURComment&_down_from_now=From+now+for&_down_minutes=$DurationInMin&host=$hostname