Help with preventing a DateTime fields from updating with NOW()

I have an app that had 2 task to be marked as complete along with the name of the person who completed the task and a DateTime stamp

TASK1 COMPLETE (Enum with Y/N)
TASK1 Completed by (user enters initials)
TASK1 DateTime (Appforumula =NOW())
TASK2 COMPLETE (Enum with Y/N)
TASK2 Completed by (user enters initials)
TASK2 DateTime (Appforumula =NOW())

If someone completes TASK 1 and saves the record then at a later time some one opens the record and then marks TASK2 as complete then the DateTime for TASK1 is overwritten with NOW().

Is there any way to prevent TASK1 DateTime from updating if it is already set ?

You could try using the ChangeTimeStamp type columns for Date Time columns of the two taska and configure them to trigger on respective Task Statuses being complete ( Y)

Sample App


Thanks !!!