A quick tutorial on keeping accurate time in Windows… Double-click on the clock in the system tray (usually in the very lower-right of your screen). There should be an “Internet Time” tab.

• If the tab isn’t there, you’re either running an ancient version of Windows, or your PC is a member of an Active Domain directory, and the system is getting its time from that. (Your network administrator wants all the PCs to get the time from the same source, which is actually a very good way to do things… But only if they’re accurate!)
• You should have the “Synchronize with an Internet time server” setting checked. (If not, check it!) The default is usually time.windows.com. This is pretty good, but we’re OCD, so we can do better. Mine is set to pool.ntp.org, which is a huge network of independently-run timeservers. (Two of my own servers are in it.) Please don’t use the nist.gov ones for your desktop: they appear to be extremely overloaded, and should really only be used if you’re providing time to other people.
• By default, Windows will check that network source once a week. (Every 604,800 seconds.) This option isn’t presented to the user, but it’s a registry setting. (I won’t get into changing registry entries, since it’s not the most user-friendly interface, and mistakes can basically ruin your computer.) But HKEY_LOCAL_MACHINE SYSTEM CurrentControlSet Services W32Time TimeProviders NtpClient is your friend here. There’s a DWORD value called SpecialPollInterval, where you’ll see the default 608400. This is how often, in seconds, it’ll query. You could put anything in here, but I’d highly encourage you to set a fairly large value. My time servers query “upstream” every 1024 seconds (~17 minutes), which keeps them within 5-15ms. Unless you need sub-second precision, I wouldn’t set a desktop machine below 3600 (once an hour). I chose 28,800, which is every 8 hours. That shouldn’t let your clock drift more than a second or two, if that. Bear in mind that you’re coming from 608,400, which is once every 7 days… Every 8 hours is 21 times as often, but still an acceptable value in my mind.
• Make sure you use the “Update Now” option to verify that your time setting works.

Obviously, this assumes you’ll be online every 8 hours… I’d imagine that Windows will just get the time time you’re online otherwise.