Stumbling around in the dark can add significant risk for searchers, so whether or not to initiate a night search is always a difficult decision. Depends on weather, terrain, last known condition of the subject and their last known position, etc.

It becomes a question of balancing the likelihood of finding and helping the victim vs the added risk to the searchers. Sometimes we will do a compromise and send hasty teams up obvious trails etc in the dark, meanwhile assembling more resources for thorough effort at first light.

Rule number one of SAR teams is "Don't become a victim yourself!" If you do you, you're no longer part of the solution, you are part of the problem.