Changing the the ClockSize advanced setting will not work for screeens which I have set up splits. It does however work for displays which do not have splits set up. Any ideas on how to fix this?

Have a look at this thread from post #27 onwards, it may help intil the devs explain it more in detail.
https://www.displayfusion.com/Discussions/View/show-only-date-not-time/?ID=84cd0946-8d09-43d6-a4cd-8049ff468bc7

Awesome that worked thanks! Your customer service is amazing!

Yep, I have used most of their software for years now, great service and friendly people.