You could create a table called tblFormTracker with 3 fields ( TimeStamp as Date/Time, User as Text, Action as Text). Now on you forms Open event create a record in the table.
docmd.runsql("Insert Into tblFormTracker(TimeStamp,User,Action)
Select Now(), Environ('UserName'),'OpenForm'")
Then in the close event use a similar SQl to create an CloseForm Record.