Revelation 20 seems to describe two separate resurrections. But didn’t Jesus say all would be raised on the same day?

The text you are referring to reads:

I saw thrones on which were seated those who had been given authority to judge. And I saw the souls of those who had been beheaded because of their testimony about Jesus and because of the word of God. They had not worshiped the beast or its image and had not received its mark on their foreheads or their hands. They came to life and reigned with Christ a thousand years. (The rest of the dead did not come to life until the thousand years were ended.) This is the first resurrection. Blessed and holy are those who share in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years (Rev 20:4-6).

This passage certainly refers to two resurrections. But how much should we understand this figuratively, and how much literally?—the big question in nearly every apocalyptic passage. The passage also raises questions about the millennium—not something to be discussed in this Q&A. But you are right. Jesus taught:

“Do not be amazed at this, for a time is coming when all who are in their graves will hear his voice and come out—those who have done what is good will rise to live, and those who have done what is evil will rise to be condemned” (John 5:28-29). The phrase “a time” is literally “an hour”—suggesting not two resurrections, but one. How about the teaching of the learned apostle Paul?

“…I admit that I worship the God of our ancestors as a follower of the Way, which they call a sect. I believe everything that is in accordance with the Law and that is written in the Prophets, and I have the same hope in God as these men themselves have, that there will be a resurrection of both the righteous and the wicked” (Acts 24:14-15).

Paul’s words could be interpreted either way, though the most natural reading is that of a single occurrence. Yet the clearest OT passage seems to indicate a single event:

… At that time your people—everyone whose name is found written in the book—will be delivered. Multitudes who sleep in the dust of the earth will awake: some to everlasting life, others to shame and everlasting contempt (Dan 12:1-2).

Considering all the passages on the topic, and with literary sensitivity to the nature of apocalyptic (as we interpret Revelation), it seems most likely that this is single event. Jesus will return, the dead will be raised, the judgment will take place, and then (and only then) humans will enter into punishment or into the eternal kingdom. A single judgment day. A single resurrection.