Hi @Giorgos
Thanks for posting your question and well done for trying out some of the function to calculate the day difference.
It seems that the function you are looking for is DateDiffWorkHours - learn more about it here -
Here is also a different example using this same function - Working time: Excluding lunch break - #2 by oskars.laganovskis
Best wishes,
Elita from support@eazybi.com