Suppose I say mincha. Later the same day, forgetting I'd prayed already, I say mincha again. This second prayer said is after the earliest time one can possibly say maariv, possibly even after sunset. ...
If you are late to Maariv and miss barchu and you normally daven slowly should you... Daven faster, even if it means saying the words with little to no Kavana so that you can say Barchu at the end. ...