It is very important for me to be current with the opening and closing times of the worlds financial markets, well 7 or so at least. The math is easy to calculate once the location I am in and the time is set, but excel won't know that, reading the system clock.

Is there a way I can have excel know what the base time is so if the sheet were opened anywhere, it would update accordingly?

=now() just won't cut it.

Perhaps accessing a time server so I know if I am in Washington how many hours to deduct for the NYSE or FTSE to open..