MarcR, this verse pictures the ascension not the resurrection. He was buried just before sundown and resurrected just before sundown.
Jesus was talking with Mary saying he had not ascended to His Father yet: John 20:16-18: “Jesus saith unto her, Mary. She turned herself, and saith unto him, Rabboni; which is to say, Master. Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God. Mary Magdalene came and told the disciples that she had seen the Lord, and that he had spoken these things unto her.”
John 20:19: “Then the same day at evening, being the first day of the week, when the doors were shut where the disciples were assembled for fear of the Jews, came Jesus and stood in the midst, and saith unto them, Peace be unto you.”
Later that same day He appeared to His disciples and they could touch Him. So, we can say for sure the ascension was on Sunday. We are given a picture of His ascension as the wave sheath day: [look up wave sheath day for yourself] when the first fruits were waved before God as a tribute. This was always done on the first Sunday after Passover.
The verse standing alone could certainly be understood that way. Let's look at the context:
1 Cor 15:1-20
Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
4 And that he was buried, and that he rose again the third day according to the scriptures:
5 And that he was seen of Cephas, then of the twelve:
6 After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep.
7 After that, he was seen of James; then of all the apostles.
8 And last of all he was seen of me also, as of one born out of due time.
9 For I am the least of the apostles, that am not meet to be called an apostle, because I persecuted the church of God.
10 But by the grace of God I am what I am: and his grace which was bestowed upon me was not in vain; but I laboured more abundantly than they all: yet not I, but the grace of God which was with me.
11 Therefore whether it were I or they, so we preach, and so ye believed.
12 Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead?
13 But if there be no resurrection of the dead, then is Christ not risen:
14 And if Christ be not risen, then is our preaching vain, and your faith is also vain.
15 Yea, and we are found false witnesses of God; because we have testified of God that he raised up Christ: whom he raised not up, if so be that the dead rise not.
16 For if the dead rise not, then is not Christ raised:
17 And if Christ be not raised, your faith is vain; ye are yet in your sins.
18 Then they also which are fallen asleep in Christ are perished.
19 If in this life only we have hope in Christ, we are of all men most miserable.
20 But now is Christ risen from the dead, and become the firstfruits of them that slept.
KJV
Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand;
2 By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain.
3 For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures;
4 And that he was buried, and that he rose again the third day according to the scriptures:
Here we have a positive statement that Jesus was raised ON THE THIRD DAY.
As we look at what follows we see Paul making a case against those who denied the resurrection from the dead.
5 And that he was seen of Cephas, then of the twelve:
6 After that, he was seen of above five hundred brethren at once; of whom the greater part remain unto this present, but some are fallen asleep.
7 After that, he was seen of James; then of all the apostles.
8 And last of all he was seen of me also, as of one born out of due time.
Witnesses to the resurrection
12 Now if Christ be preached that he rose from the dead, how say some among you that there is no resurrection of the dead?
13 But if there be no resurrection of the dead, then is Christ not risen:
14 And if Christ be not risen, then is our preaching vain, and your faith is also vain.
15 Yea, and we are found false witnesses of God; because we have testified of God that he raised up Christ: whom he raised not up, if so be that the dead rise not.
16 For if the dead rise not, then is not Christ raised:
17 And if Christ be not raised, your faith is vain; ye are yet in your sins.
18 Then they also which are fallen asleep in Christ are perished.
19 If in this life only we have hope in Christ, we are of all men most miserable.
Philosophical reasons why the resurrection is essential
20 But now is Christ risen from the dead, and become the firstfruits of them that slept.
THIS IS A POSITIVE ASSERTION OF THE RESURRECTION concluding Paul's argument
Ascribing it to the Ascension doesn't fit the context.