Had a decompression about 3 years ago - three little holes patched with hydrocolloid plasters after the op. In and out same day.
You get a nerve block, so your arm will be dead for quite a while, so you leave the sling on. Once you can move your arm, then you need to remove the sling, and use it as much as you can bear.
Getting dressed is painful, but you'll probably laugh as you struggle to get a coat on - you'll need some help at first. The key is to keep using it to get your range of movement back. I was back to 95% range within a couple of weeks.
I do alot of sport. I was off work about a month, and back into my sport after two weeks of the op and took it easy.
The recovery of 3-6 months isn't quite right, maybe 80% recovered. It was 18 months to two years before I was at 100%.
I would do it again though. It was worrying that the recovery was taking along time, but doing sport probably aggravated it.
I'm three years post surgery and my shoulder is great.