Clicking in the bottom right of the page opens the settings pane where you can adjust pretty much everything to modify the built in clocks, change captions etc, or create your own completely custom ones.

Your custom parameters are stored in the gigantic ugly URL, so you an bookmark and share your creations.

As a special Christmas treat, here's a secret BBC1 Wales Christmas clock:
https://zxnet.co.uk/clock/#template=custom:clock=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:caption=W3sieCI6Mzg0LCJ5Ijo0NTAsIm9wYWNpdHkiOjEwMCwiYWxpZ24iOiJjZW50cmUiLCJiYXNlbGluZSI6Im1pZGRsZSIsImNvbG91ciI6IiNkNWJiNjQiLCJiIjpmYWxzZSwiaSI6ZmFsc2UsInNpemUiOjEwMCwiZm9udCI6InNlcmlmIiwic3BhY2luZyI6MCwic3RyaW5nIjoiQkJDMSJ9LHsieCI6MzgwLCJ5Ijo1MjAsIm9wYWNpdHkiOjEwMCwiYWxpZ24iOiJjZW50cmUiLCJiYXNlbGluZSI6Im1pZGRsZSIsImNvbG91ciI6IiNkNWJiNjQiLCJiIjpmYWxzZSwiaSI6ZmFsc2UsInNpemUiOjYwLCJmb250Ijoic2VyaWYiLCJzcGFjaW5nIjowLCJzdHJpbmciOiJXQUxFUyJ9XQ==