Introduction
On windows based PC's, laptops and tablets the time is normally obtained from a quartz crystal based clock that is maintained by a lithium ion battery on the motherboard of your computer.
In general you can expect time drift of 2 or more seconds per day (compared to about 1 second every 3 days from a typical hardware token), but can be greatly improved if the PC is automatically synchronised with an external source (either an internet time server or the clock on the local domain controller).
Correcting the time on a windows computer
It is possible to identify the correct time (accurate to the second) by opening a windows browser to an online timer server (see examples below);
Once you have accessed the external time source you can then use this resource to check the accuracy of the clock on your local computer.
Launch the control panel by (press 
, type "control panel" then click 
)
From the control panel click on the 
icon
Select the "Date and Time" tab to display the date and time, then compare this time with the time shown from the external time server;
Ideally the two times should be within a second or two of each other but if there is significant drift you can correct the time by either using the 
button, or by selecting the "Internet Time" tab, and synchronising with an internet time server (example below);
