Hi @BS10,
This is a little out of my depth. I'm pretty new to Power Automate. I'm C sharp developer.
Can you provide some additional detail regarding how the SP list is being populated before flow triggers?
How are the records first being populated? Is it during the original item creation that the end time is calculated? Can you explain this preprocessing - original item creation? Give names of columns, like created, expired (calculated field?), end time (blank? to be populated using Power Automate?).
Hopefully, someone with more experience can chime in and provide options.