No problem for me
I own a Mac pro of the same model as the OP, and have yet to encounter a situation where the computer is not responsive to the option key at startup, even on a "hot" reboot.
Since my Tiger install is on a raided array, i cannot use the startup disk item under windows to change my startup disk (the raid array does not appear). Because of that, i have elected to keep my startup disk set on mac os, and use option to boot from the boot camp partition when needed.
However, I have found the window of time during which the computer responds to a keyboard action very small, maybe 3/4 seconds at best. This occurs right after the fans spin up.
I still occasionnaly miss it when intending to start windows, and I find it pretty annoying to wait until the os has loaded, then having to shut it down merely to try again.
Regarding the time/date issue, I think this has to do with the the way each system handles the hardware clock: Tiger sets it to GMT and then displays time according to your timezone setting, when windows simply insists on setting the hardware clock to the local timezone.