seems to depend on the type of product and operating conditions.. ymmv... I've had silicone spray oil dry up in a few weeks, and door hinges go right back to squeaking. But sitting on an O-ring that's not moving or being exposed to airflow or contaminating elements? probably won't dry up for a while.
If I don't clean the rails that the slide moves on in my pistol and just leave the bearing oil on... in about 15-20 mags it will be contaminated and dry enough that it won't cycle completely. But that's why you clean it after every use.