Our experience so far. We always do early seating dinner. We are dressed and ready well before dinner and we go to whatever bar we prefer at that time for our 3 drinks. Typically the British pub if that is what is on our ship.
We go and have our early dinner and then head to the diamond lounge. At this point, about an hour before late seating, we typically find the diamond lounge empty for about an hour and have great service and get our fill for the evening.
When the lounge opens, it is packed, but the last hour is mostly vacant from our experience.