Unable to change createdAt date to unix timestamp with mongoose

Question

The mongoose documentation has a section about changing the timestamps property who is setting a Date for createdAt and updatedAt to a UNIX timestmap.

https://www.mongoosejs.cn/docs/guide.html#timestamps

const schema = Schema({
  createdAt: Number,
  updatedAt: Number,
  name: String
}, {
  // Make Mongoose use Unix time (seconds since Jan 1, 1970)
  timestamps: { currentTime: () => Math.floor(Date.now() / 1000) }
});

My code

const userAccountSchema = new mongoose.Schema({
    email: {
        type: String,
        required: [true, 'Please add an email'],
        unique: true,
        match: [/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/, 'Please add a valid email']
    },
    password: {
        type: String,
        minlength: 6,
        select: false
    },
    is_active: {
        type: Boolean,
        default: false
    },
    onboarding_completed: {
        type: Boolean,
        default: false
    },
    confirm_token: String,
    reset_password_token: String,
    reset_password_expire: Date,
}, { 
    timestamps: { currentTime: () => Math.floor(Date.now() / 1000) }
});

The result is a record with a Date for createdAt and updatedAt instead of a timestamp.

"createdAt": "1970-01-20T03:09:20.506Z"
"updatedAt": "1970-01-20T03:09:20.506Z"

Can someone help me out?