Hi Heather, This is an interesting use case. One way I can think of to solve for this would be to use MDA and bionic rules to create a tracking table that would consist of the following fields:
Last period (week or day depending on your refresh frequency) health score
Current health score
Date of last change
After setting all Accounts with the current health score, you'd then use rules to write the value in the current health score field to the last period field, write the actual current health score to the current health score field and then if the last period and current health score are not equal, update the date of last change with the current date (if the two fields are equal, leave the date of last change alone).