ArchimedesQ Good question, let me know when you figure it out lol. For me, it’s when the changes I’m making aren’t doing much to improve anything. If I feel like the idea is good, but it’s not quite there, I’ll put it on the shelf for a month and come back to it with fresh ears.
I keep a “premaster” folder for “finished” tracks. I usually let them sit there until I don’t remember what it even sounds like (usually a month is lots as I’m working on so many tracks that old ones fade from memory pretty quickly). If I listen and it sounds finished, then it is. If something sticks out, I go back to editing and repeat the process.