If this feature is available in Quickbooks desktop and has been requested on QBO for years, it really needs to be implemented ASAP.

Since this is a known missing feature that is absolutely essential for basic bookkeeping and accounting, the steps above need more detail.

"export it into an Excel file to allow for the creation of formulas to calculate the variance between the invoice dates and their corresponding payments. Then, you can calculate the mean of these variances to find the average number of days it takes for each customer to make payments. "

How? What formulas will work? The file export does not show which payment paid which invoice or the payment date, so it's not obvious how to calculate anything between the invoice and its payment.

If this isn't possible, which third-party apps would work? Or how does our business migrate back to Quickbooks Desktop?