Welcome to the community, Mike! :grinning_face_with_big_eyes: Unfortunately Airtable’s text fields don’t support placeholders like that. If these notes are just a single note per record (i.e. each record captures info about a single event, including notes), you might consider adding a field that’s the Created Time type, which will automatically fill with the date and time that the record is made.
If, however, you’re using a notes field to capture several notes that are added at different times, then I’m afraid you’ll have to add those date and time stamps manually. However, there’s also the option of using a tool like TextExpander, where you type a pre-made key combination that inserts whatever you want. I just made a snippet that can insert the current date and time whenever I type “::dt”, like this: 07/24/2019 - 02:25 PM
This functionality exists in a lot of other software that has served the same purpose as Airtable for me in the past. I'd love to see this implemented into Airtable! OneNote, Excel, Google Sheets, Evernote, MLO, etc all already have this functionality.