Kinda. If your Customers table is set up like this
(this field will allow you to correctly process brand new customers, for whom there won’t be a “previous” date to check against. later calculations will result in a time difference of 0 days since there will just be one date compared to itself)
Set your other table up like this:
Then you could have an Automation that triggers when records in your Log table matches the conditions: the Previous Date is blank and the Comparison Date is not empty. Your automation would have a
Update Record step that copies the Comparison Date into the Previous Date, and from there your Time Diff field will do the calculation for you.
This is a flawed solution. You’ll need to make sure the date field is filled in properly. If you need to revise that date you’ll need to clear out the Previous Date field to get the Automation to re-run.
The solution also requires that records be added sequentially. Bulk adding records, and trying to bulk fix existing records, will not work. but since you are adding log records once per customer each week, this may not be an issue.