Lighting at this point will not bring about any benefits to anything but increased algae growth in your tank (nutrient levels will be very high during the cycle), unless there is some animal life on the rock that needs it provided it may survive the nitrogen cycle.

Scrubbing the rock now out of the tank will help remove some decaying matter that will otherwise just settle to the tank bottom as it falls of the rock tobe cleaned up later. Skimming at this point on the other hand is highly reccommended.