This was a fun one! You'll need to add a calculated value to your form and then use a formula like this:
formatDate(dateAddMinutes(date(1,1,1970,0,0),max([Date 1,Date 2,Date 3])/1000/60), "MM/dd/yyyy")
Replace the Date 1, 2 and 3 and just add extra commas for your other 7 fields.
- The max function gets you the right date but in the wrong format: Unix epoch, which is the number of milliseconds since January 1, 1970.
- You then divide that by 1000 to get seconds then by 60 to get minutes, then add those minutes to January 1, 1970 using the dateAddMinutes function. You may want to play with the two 0's in this function based on your timezone if time is important.
- Finally you can use formatDate to get the right string version of the date. If you need the value in an actual date control that gets harder. Didn't take my POC that far.
Good luck!