In other passages of the Bible, the phrases “ἐν ἐσχάταις ἡμέραις” and “ἐπ᾽ ἐσχάτων τῶν ἡμερῶν” are rendered as “in the last days” (2Ti 3:1; 2Pe 3:3). It is consistent to render the phrase “ἐν ἐσχάταις ἡμέραις” in the same way at James 5:3.
A lot of English translations render the words “ἐν ἐσχάταις ἡμέραις” as “in the last days” at James 5:3, giving the idea that the last days had already begun in the first century, when James lived:
English Standard Version: “Your gold and silver have corroded, and their corrosion will be evidence against you and will eat your flesh like fire. You have laid up treasure in the last days.”
New International Version: “Your gold and silver are corroded. Their corrosion will testify against you and eat your flesh like fire. You have hoarded wealth in the last days.”
International Standard Version: “Your gold and silver are corroded, and their corrosion will be used as evidence against you and will eat your flesh like fire. You have stored up treasures in these last days.”
American Standard Version: “Your gold and your silver are rusted; and their rust shall be for a testimony against you, and shall eat your flesh as fire. Ye have laid up your treasure in the last days.”
New American Standard Bible: “Your gold and your silver have rusted; and their rust will be a witness against you and will consume your flesh like fire. It is in the last days that you have stored up your treasure!”
Contemporary English Version: “Your money has rusted, and the rust will be evidence against you, as it burns your body like fire. Yet you keep on storing up wealth in these last days.”
Young’s Literal Translation: “Your gold and silver have rotted, and the rust of them for a testimony shall be to you, and shall eat your flesh as fire. Ye made treasure in the last days!”
The Bible in Living English: “Your gold and silver have rusted and their rust will be a testimony to you and will eat your flesh like fire. You have been hoarding in the last days.”
English Revised Version: “Your gold and your silver are rusted; and their rust shall be for a testimony against you, and shall eat your flesh as fire. Ye have laid up your treasure in the last days.”
New English Translation: “Your gold and silver have rusted and their rust will be a witness against you. It will consume your flesh like fire. It is in the last days that you have hoarded treasure!”
Holman Christian Standard Bible: “Your gold and silver are corroded, and their corrosion will be a witness against you and will eat your flesh like fire. You have stored up treasure in the last days.”
Common English Bible: “Your gold and silver have rusted, and their rust will be evidence against you. It will eat your flesh like fire. Consider the treasure you have hoarded in the last days.”
World English Bible: “Your gold and your silver are corroded, and their corrosion will be for a testimony against you and will eat your flesh like fire. You have laid up your treasure in the last days.”