Hello:
The very nice business class lounge in Paris CDG (do no remember the name, but it was in Shengen part and not the one by Loungekey…) let me scan the boarding pass and enter the evening before the next morning flight to AMS. (I missed my flight this year in August.)

Now the KLM lounge also had scanners where the green light lets you in, but there I was within 5 hours or so (entered OK in August).

In February, the wonderful lounge in IST let me enter for a flight after I missed my connection for 9 or 10 hours (I used Lounge Key there).

The 3 hour rule was never questioned in fact, on any of my entrances - in BCN, BUD, PRG or elsewhere. But I might not have spent more than 3 hours in these anyway.