First, disregard what I said about the time in post #705: I got my times mixed up.
His date of death--or heavenly birthday--will be accounted as April 2, 2005, the Saturday, since that's what it was, after all. (We'll see--sooner than later is my guess--what date he will have for a feast day. April 2, it turns out, is already the feast of St. Francis of Paola, though one source gives it as optional, I think, and I'm sure that the saints don't really carp about not getting the "exact dates.")
Cardinal McCarrick mentioned "Saturday" in his homily concerning the Easter Vigil; after all, the Easter Vigil most likely begins on the prior Saturday evening. If Easter (and other high feasts, BTW, like Christmas) gets the dignity of a vigil, then it's not hard to see why Sunday, the "little Easter," may get the same. (IIRC, concerning the Catholic Encyclopedia mention: Saturday evening Vigil masses didn't begin until somewhat recently, after the writing of that Catholic Encyclopedia, which is from nearly a hundred years ago. There used to be stricter limits on the time of day when masses were permitted.)
As others have already written, Saturday evening masses can fulfill the Sunday obligation. As I also wrote in #705, the first reading at the Mass now being celebrated at St. Matthew's Cathedral in Washington was for the Sunday, the homily was for the Sunday, and it's still early Saturday evening. This was around 6 pm in Washington, and the Pope died after 9 pm in Rome.
That's essentially correct.
Following the Jewish tradition of having the Sabbath begin at sunset of the previous evening, our Sunday celebration begins with First Vespers (Evening Prayer) on Saturday, and ends with Compline on Sunday night. A Mass which fulfills the Sunday obligation can be celebrated any time in between. The Vigil Mass was more common in ancient times than in more recent centuries, and the practice was revived by the Second Vatican Council, which also recommended an increased public celebration of the Liturgy of the Hours.
Vespers is nominally said around sunset or at 6pm, but there's a good deal of flexibility allowed, especially if pastoral considerations recommend an earlier time. The major hours of Lauds and Vespers can also be combined with Mass, which essentially means a recitation of three psalms (with antiphons) and the appropriate Gospel Canticle (Benedictus for Lauds or Magnificat for Vespers) after Communion.
I have found that the public celebration of the Hours is fairly rare outside of religious communities in the States, but major churches in Europe, e.g., London's Westminster Cathedral, do maintain this ancient practice, which goes back at least to St. Augustine.
As you probably know, there is a table of precedence for various feasts. This week is one continuous celebration of Easter Sunday, which does not end until Vespers tomorrow evening, and this takes precedence over all other potential feasts. This Sunday, which used to be known as Low Sunday, and is now Divine Mercy Sunday by decree of our Holy Father of blessed memory, is actually the last day of the Easter celebration.
Won't tomorrow -- the day the first Vatican mass will be said for John Paul II (9 hours from now) -- be Orthodox Easter Sunday?