Sunrise is the “birth” of the day at a particular location, and it will resonate for those persons born on that day at that location. It will resonate particularly for persons of recognition because the day of their birth is a collective experience… especially when bounded dimensionally.
It is common practice to use Noon when the birth time is unknown, arbitrarily splitting the day in half so as to arrive at an ‘average’ chart. This is problematic, because the resulting chart is just average and not tied to a collective event. Noon is not a natural event, but a construct of man’s attempt to simplify timekeeping by breaking up various zones of space into discrete intervals. As such, it is Noon throughout an entire timezone for all individuals born in that timezone. If one were to use the moment of Zenith for the Sun, now that would be a different matter.
I still prefer to use Sunrise because the Zenith of the Sun is not as evidentially obvious and therefore more ponderous. Alternately, one could use Sunset and indeed, that may be more appropriate than Sunrise for those born at night. Alas, the two will resonate on different levels of symbolical understanding, with Sunset more clearly defining relationship to the collective.
I have found the Sunrise chart to be quite effective when the birth time is unknown.