It will depended upon the product, but generalising…a lot happens in the first few days. I’d say about a month if general listening in the evening and leaving on. Speakers and cables take longer, the run-in time is the playing time only; the louder the better 
After a 3 months you’re there.
The only run-in new classic products are in the demo rooms at Naim and a select few homes. Dealer demo kit is half way there.
As you’d imagine run-in is a pain when designing products. To accelerate run-in in R&D we have a box that turns the product on, play loud, off, on, play loud, off and repeat.