Regarding you first question, we observe Ekadasi from sunrise to sunrise. The 12 midnight is western astronomical calculation, but the Vedic astronomical calculation begins either from the sunrise or the moonrise. Generally it is sunrise. Our calculation is like this: when the sunrise is there, Ekadasi tithi (date) must be there. If Ekadasi tithi is not in the sunrise and the tithi begins, say after a few minutes after the sunrise, then we accept that day as previous to Ekadasi. All our ceremonies are calculated in that way. This means we must see the tithi during sunrise.
Letter to: Madhudvisa -- England 30 September, 1969