change the multiplier, I can't remember the offset off the top of my head, but it's a hex value in the firmware.
Didn't realise the timezone was an issue, but that's just a matter of changing the UTC shift, I'll dig around when I get a chance.
As posted above, if you have no confidence in flashing custom firmwares, then please do not attempt this. It is however almost identical to flashing custom firmware on iPhones and Xboxes etc, so if you've done that in the past this should be straightforward.
I'll see if i can put some screengrabs up, as a visual aid.