Just like your smartphone, Windows 7 also checks the internet for the correct date and time and keeps your system updated with the correct time. Windows 7 periodically connects to online time servers to check for the correct time and updates yours system’s time accordingly. While this all works great, the only glitch is that Microsoft supplied time servers are overloaded (owing to the fact that millions of users worldwide use Microsoft Windows) and sometimes do not respond. What you can do is that you can set Windows to use some publicly available better time servers that respond quickly and provide the correct time.
To change the time servers in Windows 7, you will have to open the Date and Time settings. You can open them by right-clicking on the date and time being shown in the bottom-right corner of your screen and selecting Adjust date/time from the context menu. In the Date and Time settings window, select Internet Time tab and then click on the Change Settings button.
This would open another window where you can enter the new time server. While you can research publicly available time servers over the internet yourself, I would save your time and suggest that you use pool.ntp.org. After entering the new time server, you can click the OK button to save the settings.
From now on Windows 7 would connect to the new time server (which is very fast) and update your time if its not correct. If at any later stage, you want to revert back to the original Microsoft supplied time server, then just change the time server back to time.windows.com. But there are more chances that you would stick to a better and faster time server.