It depends on the crowd. Total cave length is not more than 100 meters one way (I suppose), but before entering inside the main cave, we have to be the part of a queue, that can be one kilometer long, but not more than that. If there is less crowd, and the queue moves regularly, it is possible to complete darshan within 30 minutes, but at the time of crowd or aarti, it takes upto two hours. Additionally, if crowd is much more, expect to wait outside the entry gate, sometimes upto three hours.