The difficulty an astrologer faces for casting a prasna horoscope is the time and place for casting the horoscope. Unlike the place and time of birth, time of casting a prasna horoscope is not tangible. To understand what should be right time of casting the prasna we need to understand the dynamic involved in a prasna. Prasna is a tool which makes and astrologer a true daivagna or the messenger of the divine will. Although it would looks quite arbitrary from the way it is done, there is a deep meaning behind it. Only when the time is right for the querist to know more about his question, he will be inspired by the divine will to go to a qualified astrologer. Here is the astrologer just becomes a messenger of the divine will or just an instrument in the hand of the supreme consciousness. For this to happen two conditions must be satisfied; the queries should be sincere and the astrologer should be qualified. When I say a qualified astrologer, what do I mean? Prasna Marga states it quite clearly, which I can summarize as someone who has perfected the art of natal horoscopy and has the ability to read the heavens (positions of planets in the sky) and its signs (the nimitta and shakunas- the omens) and does his spiritual practice quite ardently (to connect to the supreme consciousness without hindrance).
Like birth of any being in this world in various phased such as impregnation, conception and delivery, the question also passes through similar phases. The impregnation happens when the question crops for the first time in the mind of the querist. Then when the querist ponders on the question and searches for answers, it is the phase of conception. The phase of conception continues till the question is asked to a Daivagna. However the delivery of the question didn't occur yet as it is still in the process of delivery. Only when the Daivagna is inspired to draw a horoscope to that query, the query is said to be delivered. Since the medium of delivery is the Daivagna, the time at which he is inspired and his location at that moment is important in drawing up the query. At the time when the Daivagna gets the question, the happening in his surrounding offers cues to the nature of the question and the possible outcome, which are covered under shakuna shastra (the omens) and hence the Daivagna should be quite observant of any such cues.