Hi,
yes there is a way e.g.: Set downtime for 2 hours:
curl --insecure "http://YourCMKHost/YourSite/check_mk/view.py?_do_confirm&_transid=-1&_do_actions=yes&_username=YourUser&_secret=YourSecret&view_name=hoststatus&host=YourTargetHost&_down_2h=2+hours&_down_comment=COMMENT"
Remove the downtime:
curl --insecure "http://YourCMKHost/YourSite/check_mk/view.py?_do_confirm&_transid=-1&_do_actions=yes&_username=YourUser&_secret=YourSecret&view_name=hoststatus&host=YourTargetHost&_down_remove=Remove"
Karl