SpriteKit moving Nodes faster with time - ios

Question

I want to spawn the Objects faster with time, for e.g. I got a Object added every 1.5 seconds. This Object is moving to X = -100 with Duration = 5. After 30 seconds it should move faster.
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
.....
SKAction * Spawn = [SKAction performSelector:#selector(Enemy) onTarget:self];
SKAction * Delay = [SKAction waitForDuration:1.5];
SKAction * SpawnThenDelay = [SKAction sequence:#[Spawn, Delay]];
SKAction * SpawnThenDelayForever = [SKAction repeatActionForever:SpawnThenDelay];
[self runAction:SpawnThenDelayForever];
.....
}
- (void)Enemy {
Enemy = [SKSpriteNode spriteNodeWithImageNamed:#"Enemy.png"];
Enemy.size = CGSizeMake(85, 85);
Enemy.zPosition = 2;
Enemy.name = #"Enemy";
Enemy.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:CGSizeMake(50, 50)];
Enemy.physicsBody.dynamic = NO;
Enemy.physicsBody.allowsRotation = NO;
Enemy.physicsBody.usesPreciseCollisionDetection = YES;
Enemy.physicsBody.restitution = 0;
Enemy.physicsBody.categoryBitMask = EnemyCategory;
Enemy.physicsBody.collisionBitMask = StoneCategory;
Enemy.physicsBody.contactTestBitMask = StoneCategory;
Enemy.position = CGPointMake(self.frame.size.width * 1.25, self.frame.size.height / 2.2);
SKAction * actionMove = [SKAction moveToX:-100 duration:5];
SKAction * actionMoveDone = [SKAction removeFromParent];
[Enemy runAction:[SKAction repeatActionForever:[SKAction sequence:#[actionMove,actionMoveDone]]]];
[self addChild:Enemy];
}

Answer 1

every SKAction has a property speed and by defult every action runs with a speed of 1 so you can increase speed property acc to your game situation

Answer 2

You could store your enemy speed as global variable and add a NSTimer with a 30 seconds interval and every 30 seconds, the timer executes a function that adds a certain value to the speed of the enemy. But make sure there's a speed limit otherwise it will be too fast.
MyScene.h:
#import <SpriteKit/SpriteKit.h>
#interface MyScene : SKScene {
NSTimer *timer;
int SpeedVar;
int MaxSpeed;
int IncreaseSpeedValue;
}
#end
MyScene.m:
-(id)initWithSize:(CGSize)size {
if (self = [super initWithSize:size]) {
timer = [NSTimer scheduledTimerWithTimeInterval:30.0 target:self selector:#selector(increaseSpeed) userInfo:nil repeats:YES];
SpeedVar = -100; //Normal speed of your enemy
MaxSpeed = -300; //Maximum speed of your enemy
IncreaseSpeedValue = 15; //Increase speed by this value every 30sec
}
return self;
}
-(void)increaseSpeed {
if (SpeedVar > MaxSpeed)
SpeedVar -= IncreaseSpeedValue;
else {
[timer invalidate];
timer = nil;
}
}