Well, Two Bees, this, I'm sure is when you'll start the beginning of interpreting things for yourself. Your going to get 10 beekeepers give you 11 different opinions.
My Opinion: If you notice bees (3-4 of them) having to wait when they fly in, because the hole is being used, then its too small. Usually I leave the entrance reducer on for a good week to two weeks when I first install them. The reason they are crowding the front entrance is because its too warm in the hive. (AKA they are having a smoke and a brew on the deck) So, go ahead and open it up to that second opening.
Its all interpretation - its not like you'll kill the entire hive because you don't open it up at the right time. If you think the bees are not ready, then don't do it. Use YOUR judgement, because a lot of people from hundreds of miles away cannot always be right. (Although we mostly are ;))