Originally Posted by FenwayTim

I wouldn’t get there early just to get to the new(er) Delta lounge, but to give you a data point, you can leave the Delta lounge in Terminal A, walk to train (better then the waiting for the bus if your any kind of a walker), get on the train and be at the security entrance in Terminal B for your flight in ~17 minutes. Thats a brisk walk but by no means a jog. Really the only wildcard is if you can get on the train right away because its there or you wait 2-4 minutes for the next one..
If you have luggage your checking, best to do that at Terminal B at the AF desk and then you can determine at that point what kind of effort you want to make to get to the DL lounge.