You need to do it manually, best time is on initial network creation.
The TZ defaults to the template value but isn't bound to it, so you can change it without unbinding.
You could use the API to automate doing it, but for 60 networks it's probably quicker to do manually as it's a one-off.
Note that as well as the TZ, there is a separate Country/Region setting.
The Country/Region setting can autodetect based on public IP and equipment shipping details, but it is not always correct.
C/R setting determines wireless regulatory domain and possibly local compliance, make sure both TZ and C/R are set correctly.