Maybe I can reverse-engineer your question. Let's say we have,

TestDataset =
  Dataset[
    {<|"hcont" -> DateObject[{2022, 10, 14}], "hdeb" -> DateObject[{2022, 10, 13}]|>,
     <|"hcont" -> DateObject[{2022, 10, 12}], "hdeb" -> DateObject[{2022, 10, 11}]|>}]

I can apply a function to each of the rows, maybe something like this,

TestDataset[All, <|"hcont2" -> #hcont, "hdeb2" -> #hdeb, "diff" -> (#hcont - #hdeb)|> &]

Is that the kind of thing you're trying to do?

I would you suggest that you pare this down to a minimal example that demonstrates the exact place where you're having struggles. Like, maybe provide a one line expression that doesn't work as you expect along with the "correct" result that you're looking for. As it stands, it looks like I must first figure out all of your variables before I can even parse your question.