You can either change the field you display the Notes field on the layout to be a Calculation that simply references the notes field, this will allow users to lick into it scroll and copy text, but not edit, then have a global field under the field, or scripted to be in a pop-up, and the user inputs there note in the global and clicks a Submit button that runs a script to set the Notes field, which is not on the layout with the following calculation
Let ( date = Get ( CurrentDate ) ;
MonthName ( date ) & " " & Day ( date ) & ", " & Year ( date ) & ": " & Get ( CurrentTime ) & "¶¶" &
& "¶¶--¶¶" &
Or however you want that formatted.
That should do it.
Another option is a separate table and do not allow modification to the Note field in the separate table in Access and Privilages and display the notes in a portal. Let me know if you want to go down this and need some pointers.
Given the level of complexity you want to implement. It might be much simpler to capture your notes in a series of records in a related table. Each record would represent one such entry. You could then place a date field in this table set to auto-enter a date when a new portal row (new related record) is created by typing in the note field. Locking completed entries could be implemented more easily as well.
These logged entries could then be displayed in a portal.