Hi,
Yes, RUT240 should set its timezone according to cellular tower, but there's an option missing in WebUI, which I already reported to RnD.
As for RUT240 acting as NTP server - you can use its local IP or public IP (if the SIM has the public IP). Local IP will work only if camera is connected to RUT240 by LAN, and Public IP should work in any case as NTP server should open the ports itself.
EB.