Handle the time

GameScene.swift

// omitted
class GameScene: SKScene {
    // omitted
    
    // timers
    var lastTime = 0
    var currentTime = 0
    
    override func update(delta: CFTimeInterval) {
        // loop all enemies and make then walk to collide with the plyer
        for enemy in enemies {
            enemy.position = CGPoint(x: Double(enemy.position.x) - 5, y: Double(enemy.position.y))
        }
        
        currentTime = Int(delta)
        
        if (lastTime == 0) {
            lastTime = currentTime
        }
        
        if (currentTime > (lastTime + 1)) {
            lastTime = currentTime
            spawEnemy()
        }
    }
    // omitted
}