Restrict Editing When Initially Allowed

[Danny_9]

Hi,

I have created a button that sets the time for “arrived on site”. This is on the _Details screen.
The edit screen(_Form) is used to upload photos. I have restricted everything else except the “arrived on site” time.

However, when on this editing screen. The “arrived on site” can be changed.
I don’t want to allow this to be changed once it has been set.

I want to log the time and not have it changed to hide lateness.
I have tried to not allow editing of this cell but this errors the app.

The only time I want this cell to be edited is when the button is pressed as mentioned above.

Is it possible to restrict the editing on the edit (_Form)?
Or just allow the button to be pressed only once?

Thank you.