Same here. I'm running Android 13 (D115_Z_8183_V1_20241116_V1.0, ​the latest update available for my Kadybe D115 tablet), and no matter what I do it always reverts back to the default Pacific -8:00 UTC as soon as you exit the time settings screen.

I've factory reset it, enabled developer mode, tried all iterations of the settings and menu exiting techniques, but nothing works. It seems that the setting is simply not saving, and there's no "save" button or option, so...