proper way to change network time/timezone

Hello openbsc community! We are encountering the ff issue: When using basic phones, we have observed that the timestamps on the SMS are in UTC, even if we changed the linux system timezone to a different one. Also, if the basic phone will do an auto-update of date and time from the network, it will use the time in UTC. Do you have suggestions on how to change the network timezone configuration for the osmo-nitb? There is a timezone command mentioned in the osmo-nitb vty reference manual (timezone <-19-19> (0|15|30|45), ex. timezone 8 0 ). If we put that config under the BTS level (in osmo-nitb.cfg), osmo-nitb will complain that there is a config error. If we put that under the network level, osmo-nitb does not complain, but it doesn't seem to work as expected. Let me know if addtl info is needed. Thank you in advance!