Unfortunately, accurate time will be the least of your worries in another month when support for XP totally ends, and you won't want a disabled firewall. It might be better to focus on the bigger issues of planning for XP end-of-life and come back to the clock if you will be continuing to use XP and have contingencies in place to support it.
I've already encountered some of the EOL issues on an old XP that I keep around just so I can use some old peripherals. I recently needed to run SFC /Scannow to check for possible corruption in Windows. That utility requires the original Windows CD (at least on XP). On that computer, XP came preloaded from the factory and the protection was a partition containing a recovery version of Windows; no CD. Bottom line: short of reinstalling Windows, there is no way to check for corruption. Support still has a month to go but Microsoft's answer was, "Sorry, Charlie, you're SOL".
It is going to become increasingly hard to rely on XP. It has become a "disposable" operating system--you can keep using it until you have a problem, then plan on tossing it. I wouldn't worry about the clock. I'm just saying.