I just used a lounge pass for the first time when I had a painfully long layover at the Copenhagen Airport. It was great! For someone who travels often, I’m a total newbie to airport lounges, so I was really excited to have a place to hang for a few hours, where there were complimentary snacks and drinks and comfortable places to sit. Only downside is that yes, many lounges close relatively early, so if you’re on a red eye flight, you probably won’t be able to use the pass.
No, it has to be used before your flight, not after but it doesn’t matter whether it’s a connection or just a single flight. You need to show your boarding pass and booking voucher.