Whether it is necessary to start the hike up Langley before dawn is debatable. I have NEVER started a hike up Whitney or Langley before dawn, and done fine. On the trail, you will find a fair number who agree with me on this. But on the internet, the preference for an alpine start is virtually unanimous. I consider this to be more a matter of such things as the weather forecast and personal preference than anything else. Simply put, if you feel the NEED to get an early start on Whitney, you will probably want to do the same on Langley.
As for difficulty, the two are rather different. Distance is about the same. But that’s really about it. Altitude gain is significantly less on Langley. But bear in mind that almost all of it comes near the end of the hike. The first few miles at Langley actually involve almost no climbing. You climb a little as you approach Cottonwood Lakes. But you don’t REALLY start to climb until you start to near New Army Pass. And as you make the final climb up Langley, things get quite steep - FAR steeper than anything on Whitney. This whole ‘saving the steepest climb till the end’ thing can make Langley more difficult than Whitney for some.
As for scenic beauty, this is largely a personal preference thing. The first few miles of the hike up Langley can be somewhat monotonous for many. It’s a nice hike through the woods. But there is not too much to see. The hike through Cottonwood Lakes is nice. But so is Whitney. Which is nicer? Again, what do you like? After New Army Pass, the hike is largely a spectacular climb through alpine terrain. In this respect, it is somewhat similar to Whitney after Trail Crest. However, in my opinion, Whitney after Trail Crest is more rugged and spectacular. But you be the judge. In any case, the hike up Langley is FAR from shabby. | 
