It would be simplest to set up a portal to a related table where a script creates a new record each time CommitRecords occurs on your layout.
Do you know how to create and use a portal?
A date field in the portal's table can auto-enter the creation date so just creating the record in this related table is all you need do to log the modification date.
Do you know how to create scripts in Manage | Scripts?
Portal, yes. Script, maybe. I'll muddle away a bit before I come begging again. Thanks.