UIView关键帧动画计时不符合预期

我有一些动画(可在操场上测试):

import UIKit
import XCPlayground
import PlaygroundSupport
PlaygroundPage.current.needsIndefiniteExecution


let view = UIView()
view.frame = .init(x: 0, y: 0, width: 150, height: 150)
view.backgroundColor = .orange
let hand = UIView()
view.addSubview(hand)
hand.frame = .init(x: 0, y: 0, width: 10, height: 10)
hand.center = view.center
hand.backgroundColor = .green
PlaygroundPage.current.liveView = view

let fadeDuration: TimeInterval = 0.4
let translationDuration: TimeInterval = 1
let resetDuration: TimeInterval = 0.25
let duration: TimeInterval =
    7 * fadeDuration +
    4 * translationDuration +
    3 * resetDuration
var currentTime: TimeInterval  = 0.0

func addKey(_ animations: @escaping () -> Void, animationTime: TimeInterval) {
    UIView.addKeyframe(withRelativeStartTime: currentTime / duration, relativeDuration: animationTime / duration, animations: animations)
    currentTime += animationTime
}

func fadeIn() {
    addKey({
        hand.alpha = 1
    }, animationTime: fadeDuration)
}

func fadeOut() {
    addKey({
        hand.alpha = 0
    }, animationTime: fadeDuration)
}

func translate(_ direction: (CGFloat) -> CGFloat) {
    let x = direction(50)
    addKey({
        hand.transform = .init(translationX: x, y: 0)
    }, animationTime: translationDuration)
}

func reset() {
    addKey({
        hand.transform = .identity
    }, animationTime: 0)
    currentTime += resetDuration
}

UIView.animateKeyframes(withDuration: duration, delay: 0, options:  .calculationModeLinear) {
    translate(-)
    fadeOut()
    reset()
    fadeIn()
    translate(-)
    fadeOut()
    reset()
    fadeIn()
    translate(+)
    fadeOut()
    reset()
    fadeIn()
    translate(+)
    fadeOut()
} completion: { _ in
    PlaygroundPage.current.finishExecution()
}

我希望每一个 translate() 动画以相同的速度运行,但是由于某些原因,第一个和最后一个动画特别慢,尽管使用了 .calculationModeLinear

如何做到 translationDuration duration 时间是恒定的吗?