changing time zones

The time zone in my basic computer set-up it’s Australia, but the default in the Calc is US. This means I have to manually change 25-30 spreadsheets. Not good.

Regards
William

“The time zone in my basic computer setup … but the default in the Calc is US.”
On what actions and in what way does the “default in Calc” show up?
(There are 4 continental US time zones +5.)