As per my understanding on audit trails, user might want to view the details like user id, user name, transaction done (adding data/deleting/removing) and the date_time of the transaction.
These details can be provided in the form of report/ in grid view with option to filter the list of data being displayed based on the user_id/transaction name/date range/time range.
Only selected users will be having the option to view the report.
My experience: I have included this facility in all my projects (sales and inventory, invoicing, receipt collection, HRMS, Payroll etc.)
Regarding the delivery time, i would like to know how many forms are there where the audit trail has to be embedded. An application having around 25-30 forms will require 8-12 hrs of work.