I think heaven was opened at Easter or a little before, not at the ascension. For Jesus already entered heaven after he died. He descended to hell, liberated the souls from the Limbo of the Fathers, and then went to heaven (spiritually) with the saints of old testament times, before Resurrecting in a glorified body. His ascension into heaven was his bodily ascension, but it was not the first time he had been.
In his Summa Theologica, Aquinas says that they went to heaven after Christ left hell. So somewhat before his Resurection even:
"Consequently, when Christ descended into hell, by the power of His Passion He delivered the saints from the penalty whereby they were excluded from the life of glory, so as to be unable to see God in His Essence, wherein man’s beatitude lies, as stated in the I-II, 3, 8]. But the holy Fathers were detained in hell for the reason, that, owing to our first parent’s sin, the approach to the life of glory was not opened. And so when Christ descended into hell He delivered the holy Fathers from thence. And this is what is written Zach. 9:11: “Thou also by the blood of Thy testament hast sent forth Thy prisoners out of the pit, wherein is no water.” And (Col. 2:15) it is written that “despoiling the principalities and powers,” i.e. “of hell, by taking out Isaac and Jacob, and the other just souls,” “He led them,” i.e. “He brought them far from this kingdom of darkness into heaven,” as the gloss explains. "
D"irectly Christ died His soul went down into hell, and bestowed the fruits of His Passion on the saints detained there; although they did not go out as long as Christ remained in hell, because His presence was part of the fulness of their glory. "
At the Last Supper, even before the crucifixion, the disciples ate the flesh of Jesus (this is my flesh…), the resurrected, glorious Jesus. How this can be we cannot know, only apprehend by faith.
Not necessarily. Aquinas was of the opinion that they recieved his visible body invisibly and his passible body impassibly…by nature of the sacrament.
He also believed that if it had been consecrated on Good Friday, his body and blood would have been dead and seperate in the sacramental species:
From his Summa Theologica:
“Christ’s body is substantially the same in this sacrament, as in its proper species, but not after the same fashion; because in its proper species it comes in contact with surrounding bodies by its own dimensions: but it does not do so as it is in this sacrament, as stated above (3). And therefore, all that belongs to Christ, as He is in Himself, can be attributed to Him both in His proper species, and as He exists in the sacrament; such as to live, to die, to grieve, to be animate or inanimate, and the like; while all that belongs to Him in relation to outward bodies, can be attributed to Him as He exists in His proper species, but not as He is in this sacrament; such as to be mocked, to be spat upon, to be crucified, to be scourged, and the rest.”
“As was said above (76, 2), in virtue of the consecration, the body of Christ is under the species of bread, while His blood is under the species of wine. But now that His blood is not really separated from His body; by real concomitance, both His blood is present with the body under the species of the bread, and His body together with the blood under the species of the wine. But at the time when Christ suffered, when His blood was really separated from His body, if this sacrament had been consecrated, then the body only would have been present under the species of the bread, and the blood only under the species of the wine.”
“Christ’s soul is in this sacrament by real concomitance; because it is not without the body: but it is not there in virtue of the consecration. And therefore, if this sacrament had been consecrated then, or reserved, when His soul was really separated from His body, Christ’s soul would not have been under this sacrament, not from any defect in the form of the words, but owing to the different dispositions of the thing contained.”
The Bread PRIMARILY becomes his body…and is only his blood, soul, and divinity because they are now substantially united.
The Wine PRIMARILY becomes his blood…and is only his body, soul, and divinity because they are now substantially united.
But on the days before his resurrection, his presence in the eucharistic species would have been the same as his visible self, except impassible and invisible…but this is by the nature of Transubstantiation…not by nature of his body