The F message provides the ntp server information. The f command sets the NTP server.
The current NTP settings are shown after a sending f: to the Cube
F:ntp.homematic.com,ntp.homematic.com\r\n
by default the ntp.homematic.com server seems to be used.
Updates can be done via the f:[ntp server1],[ntpserver 2], Cube responds with an F: message containing the new ntp servers
e.g.
f:
F:ntp.homematic.com,ntp.homematic.com
f:nl.pool.ntp.org,ntp.homematic.com
F:nl.pool.ntp.org,ntp.homematic.com