Default values are hostnames like 0.pool.ntp.org, 1.pool.ntp.org .
But if in UI set an IP of NTP server, it is not accepted, see the attached screenshot.
{"build_id": "2015-04-13_22-54-31", "ostf_sha": "c2a76a60ec4ebbd78e508216c2e12787bf25e423", "build_number": "310", "release_versions": {"2014.2-6.1": {"VERSION": {"build_id": "2015-04-13_22-54-31", "ostf_sha": "c2a76a60ec4ebbd78e508216c2e12787bf25e423", "build_number": "310", "api": "1.0", "nailgun_sha": "d22c074dec091e5ddd8ea3003c37665058303cd5", "openstack_version": "2014.2-6.1", "production": "docker", "python-fuelclient_sha": "9208ff4a08dcb674ce2df132399a5aa3ddfac21c", "astute_sha": "d96a80b63198a578b2c159edbd76048819039eb0", "feature_groups": ["mirantis"], "release": "6.1", "fuelmain_sha": "335d3ed09ed79bd37e1f7a90442c4831c8845582", "fuellib_sha": "8b80657e9ceed8d59c2dff1c11e1481c7e69380e"}}}, "auth_required": true, "api": "1.0", "nailgun_sha": "d22c074dec091e5ddd8ea3003c37665058303cd5", "openstack_version": "2014.2-6.1", "production": "docker", "python-fuelclient_sha": "9208ff4a08dcb674ce2df132399a5aa3ddfac21c", "astute_sha": "d96a80b63198a578b2c159edbd76048819039eb0", "feature_groups": ["mirantis"], "release": "6.1", "fuelmain_sha": "335d3ed09ed79bd37e1f7a90442c4831c8845582", "fuellib_sha": "8b80657e9ceed8d59c2dff1c11e1481c7e69380e"}
