Hey there! I’m massively hitting a wall with something that might take a script?

I’m creating a Production Planner/Tracker for a YT Channel and want to have a formula that spits out the current date & time of when the {Production Status} is changed to “Post-Production” so that I have a {Post-Prod. Start Date}.

That worked fine with: IF({Project Status} = "Post-Production",LAST_MODIFIED_TIME(), BLANK())

The problem comes when I have to switch the {Production Status} to “On Hold” or “Complete”. It obviously removes the {Post Prod. Start Date} Value. And in the case of “On Hold” it will then go on to replace it with a new date and time if/when the project gets set back to “Post-Production”.

So my question I guess is, how do I get the formula to only run the first time around - or what other work-around is there?

I hope this makes sense

Thanks in advance!

Sharon