Not read the thread but, for my money, the 'transition' takes minutes/a lifetime.
You can play a convincing fretless part within moments; it really isn't that hard. But, for the next couple of decades, you will ebb and flow in term,s of the relationship you have with your own intonation. For me, it all gets a bit lairy up the dusty end where a couple of mil can make the difference between the smell of freshly mown grass and a fart in a space suit. It's a life long quest.