virtualbox.org

Hello,

this may be a stupid question, but I need to change the system time before the operating system starts (boot). I don't know how to get into the bios menu (if there is one at all) and if I try to change the time after the OS has booted, it is automatically resetted to the correct one. Is it possible to disable this "function"?

You have to remove the GA in the VM for this.

The manual (section 9.15) mentions a TSCTiedToExecution option, but I think that may cause clock skew.

Try this (undocumented) setting while the VM is shutdown: <nanoSeconds> is a signed 64 bit integer being the offset from UTC (I think)
Set it to -86400000000000 to offset the VM time back one day.

The clock ticks will then still be in sync, but with an offset applied.

Edit: This can also be set using: ... this should set the VM clock to be in sync with the host clock, but <msec> (milliseconds) offset. Negative numbers put the VM clock in the past, positive numbers put the VM into the future.