Certain sites that have live events require your device's clock to be synchronized with the country it is situated in.
Aside from that, some sites that have on demand content, such as All4 may also require you to change your time zone.
For example, to access LIVE streaming in BBC ONE, you will need to change your timezone ie time & date settings to match that of the UK.
The steps below were tried on a Windows 10 computer, but the principal should be the same for all versions of Windows, albeit a slightly different interface.
1) Right-Click on the system clock icon at the bottom right corner of your Windows computer.
2) Click on Adjust date & time.
3) By default, you should be in the Date and Time tab . Click on the Time zone drop down box.
4) Now select the timezone that you desire and close the window.
5) Click OK again.