Thanks to terror fears the ceremony will not take place every day, while the Saturday tradition is canceled at Windsor Palace.
The famous changing of the guard at Buckingham Palace in London has undergone changes because of fears it could be targeted for terrorism. Meanwhile, the similar Saturday ceremony at nearby Windsor Castle was canceled indefinitely.
The decisions were taken after recent terror strikes in Europe such as the truck attacks in Nice and Berlin last year.

Armed police officers now accompany the ceremony at Buckingham Palace, while checkpoints surround the area. The spectacle only takes place at Buckingham Palace on specific days rather than alternate days as was the custom for decades. It was also moved half an hour earlier so as not to clash with the extra traffic at lunchtime.
And just in case there isn’t a ceremony next time you’re in London here’s a reminder:
Source: Changing Changing the Guard at Buckingham Palace | Clarion Project