My primary goal tonight is to get there and not get lost, which is why I was thinking the out-and-back would be a good option.
Ok then, the easiest will be to park at the top of Skyline. Cross the road and ride on the road about 1/2 mile or less, you will see the Cannonball trailhead on your right side a red circle with a white C, follow that until you come out to a clearing with some Gas pipes. You can go straight into a Yellow trail which is very rocky uphill (it is nice coming down but a pain going up) or you can go right a little and you will see an unmarked doubletrack. Both are kinda blocked by big boulders. This is easier climb, follow it until you come out to the pipeline, keep going straight until you see a cannonball trailhead on your right (you can take that which has a nice hard climb) or keep straight until some kind of station there, make a right onto yellow. Both Cannonball and Yellow will meet at the same point on top of the climb (yellow is easier climb IMO). After that you are on top and both trails are the same, keep going straight, you will hit a nice drop shortly after both trails meet, you can go around it if you are unsure. Eventually you will hit a "Y" where Cannonball & Yellow split. I prefer Yellow because it is more technical and also because Cannonball will bring you to one of the boy scout camps and they dont like MTB's, eventually Cannonball is double track and fireroad until you get to Bear Swamp (but that is kinda far for an afternoon ride with no lights). So going back to Yellow, you can keep going and you will hit very nice technical sections. I don't know your pace, but if you make it all the way to the lookout , nice big rock (you can't miss it). I would probably turn back there or turn back whenever you feel you had enough and just follow the same directions back. I think Yellow & Cannonball are pretty well marked, so as long as you stay on those you should be fine. You might see RED, ORANGE and GREEN trail blazes but that's a whole other loop that can get complicated for a short ride
I love the yellow trail I wish I could ride today, but I am going to the Yankee game
I hope you find the trails ok.