Brief Accounting has the option to print Accounts Receivable Statements to file, which can be opened with Excel. This allows you to view the amount of interest accrued at whatever date you choose.
Choose the A/R module > Statement tab and pull up the matter in question
Make sure that the Outstanding items are displayed (O/S side menu option)
Click the Print icon
Check Statement of Account
Select Print to File
An XLS file will be created.
Now open the file using Excel. It shows you the interest total in column N.
You can change the date in cell N4 to see what the interest would be as at different dates: