Code for Godot 4 inside

Tweens

func _ready() -> void:
	animation_player.play("Work")

	var tween := get_tree().create_tween()
	tween.tween_property(animation_player, "speed_scale", 1, BOOTUP_TIME)
	tween.tween_property(shaft, "modulate", Color(0.5, 1, 0.5), BOOTUP_TIME)