Does how long you keep a stretcher in affect if it will return to normal after taking it out?

You can do a stretch once every 2-3 weeks at smaller size such as where you are, 3mm is rather small and will completely go back to normal without a question. As long as you are taking your time and letting them heal for 2-3 weeks between sizes you should be fine. I would recommend not skipping sizes so you should have gone from 2mm to 2.6mm to 3mm but what's done is done. Most people say your ears will heal back to normal all the way up to 8mm as long as you take your time