There are a few similar examples that can get you there, for example:
and
https://hub.knime.com/hanss/spaces/Public/latest/forum_flows/Calculate%20working%20days
The second one I think is easier to understand and follow along.
I modified it slightly, updating some of the deprecated nodes and replacing the Rule Engine node with a Joiner node which brings in the idle times per work day. This means you don’t have to hardcode any rules.
The end result is:
You should be able to make the modifications to calculate active hours.