Last weekend started here in Brazil, our summertime. I changed the configuration using the CLI timezone set, and forced a sync with our ntp server.
The clock on CLI is ok, but the clock on GUI hasn't changed.
Do I need to do something else?
Since there is no option in the GUI to configure the time, this seems to be a software bug to me. You should contact Cisco TAC to get this fixed, in case the reboot does not fix it. Even if its fixed after ther reboot, it would still be considered a bug I guess.