Can you elaborate?
I’m assuming you have 12 records in your table… one record for each user. Those records contain a decimal value and now you would like to convert it as duration. If you add one extra column with that formula (in app formula field), it will do the conversation at the same time when that record is created and decimal value is added.
Also, what happens if the “crono” reach 99:59:59, is going to grow on houndreds of hours? 100:00:00