Unable to perform standard calculated metric between two dates

Hi Team, I have two custom date fields on my ticket forms used for Urgent priority tickets, the fields are called:

Production Down Start Date 

Production Restored Date

I am trying to calculate the “Downtime Duration” in days by subtracting one from the other using this formula: DATE_DIFF([Production Restored Date - Timestamp], [Production Down Start Date - Timestamp], "days")

I get the following error:

I've tried a number of calculations (SUM, MED, AVG, COUNT) and different date formats (Timestamp, Date, Hour, Day of Week, etc) and no luck on any of them.

Any tips or suggestions on how to calculate this? I need to then also calculate the median per ticket as a seperate calculation.