@Tobin_Perry Here is a video response I got from the support of Airtable. (I was having a similar need than you).https://share.support.airtable.com/bLu5RL0Q Hope it helps 

Hey Tobin_Perry,I'd suggest you create a formula field with:IF ( {Field_with your dates} , {Field_with your dates}, LAST_MODIFIED_TIME ( {Name of the field with checkbox} ) )This will check if you have a date where you have been writing dates,If ther...