Throcker,
MR is mostly hikeable at night until Iceberg lake. My partner and I hiked Whitney Thursday-Saturday (March 20-22). We got a late start Thursday afternoon and made it to LBS lake at almost 2200. After summitting on Saturday, we departed our Iceberg lake camp at 1710 and made it to the car around Meysan parking area at 2335.
Navigation was most difficult below LBS lake as much of the snow had melted, making the trail hard to follow (keep in mind, it was our first time on the MR). I highly recommend not going past Iceberg lake at night, especially past the notch. We were sweating it enough in the daylight. It might not be as hairy once the snow is gone, but I bet patches of concealed ice go easily unnoticed with just a headlamp.
I'd also like to say thank you to the members of the California Mountaineering Club who also summitted Saturday. Your climbing suggestions made a difference.
Dustin