Why is setting a .text property messing with NSTimers - ios

Question

I'm programming a game in xcode 7 using swift and it is an endless game where you avoid falling objects. I have an NSTimer:
#IBAction func startNow(sender: UIButton) {
player.center.x = 160
explosion.center.x = 1000
explosion.center.y = 1000
for f in r {
random = Int(arc4random_uniform(350))
f.image = UIImage(named: "blueSQ1")
if random == 20 {
f.image = UIImage(named: "moneyRain")
}
}
random1 = Int(arc4random_uniform(5))
if random1 <= 3 {
r10.image = UIImage(named: "blackSQ1")
}
slider.value = Float(player.center.x + 122)
shieldImg.image = UIImage(named: "nil")
ad = 1.5
moveDown.invalidate()
speed1 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed2 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed3 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed4 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed5 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed6 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed7 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed8 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed9 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed10 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed11 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed12 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed13 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed14 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
speed15 = ad + CGFloat(Float(arc4random()) / Float(UINT32_MAX))
for x in r {
x.center.y = 55
x.center.x = CGFloat(20+arc4random_uniform(285))
}
moveDown = NSTimer.scheduledTimerWithTimeInterval(0.015, target:self, selector: Selector("updatePos"), userInfo: nil, repeats: true)
timeyWimey = NSTimer.scheduledTimerWithTimeInterval(0.1, target:self, selector: Selector("incrementTime"), userInfo: nil, repeats: true)
checkShield = NSTimer.scheduledTimerWithTimeInterval(0.1, target:self, selector: Selector("ifShielded"), userInfo: nil, repeats: true)
}
func incrementTime() {
timer+=0.1
scoreProgress.setProgress(Float(timer/highscore), animated: false)
//time.text = "Time: \(timer)"
}
func updatePos() {
start.center.y = 10000
startOut.center.y = 10000
coinsLabel.center.y = 10000
buyShieldOut.center.y = 10000
ifDone()
r1.center.y += speed1
r2.center.y += speed2
r3.center.y += speed3
r4.center.y += speed4
r5.center.y += speed5
r6.center.y += speed6
r7.center.y += speed7
r8.center.y += speed8
r9.center.y += speed9
r10.center.y += speed10
r11.center.y += speed11
r12.center.y += speed12
r13.center.y += speed13
r14.center.y += speed14
r15.center.y += speed15
for q in r {
if ((q.center.x)+3 > player.center.x - 15) && ((q.center.x)-3 < player.center.x + 15) && ((q.center.y)+3 > player.center.y - 15) && ((q.center.y)-3 < player.center.y + 15)
{
if (shield == 0) && ((q.image == UIImage(named: "blueSQ1")) || (q.image == UIImage(named: "blackSQ1")))
{
explosion.center.y = 10000
explosion.center.x = 10000
start.text = "RESTART"
start.center.y = 289
timeyWimey.invalidate()
y = Float(round(10*timer)/10)
timeOut.text = "Previous time: \(y)"
coins += Int(y*10)
coinsLabel.text = "Coins: \(coins)"
if y > highscore {
highscore = y
}
highTime.text = "Best time: \(highscore)"
startOut.center.y = 289
coinsLabel.center.y = 130
buyShieldOut.center.y = 167
moveDown.invalidate()
timer = 0
}
if shield == 1 && q.image == UIImage(named: "blueSQ1")
{
activated = true
}
if q.image == UIImage(named: "moneyRain") {
coins += 500
q.image = UIImage(named: "whiteSQ")
}
if q.image == UIImage(named: "green2") {
}
}
}
if ((explosion.center.x)+18 > player.center.x - 15) && ((explosion.center.x)-18 < player.center.x + 15) {
if shield == 1
{
shield = 0
activated = false
}
start.text = "RESTART"
start.center.y = 289
timeyWimey.invalidate()
y = Float(round(10*timer)/10)
timeOut.text = "Previous time: \(y)"
coins += Int(y*10)
coinsLabel.text = "Coins: \(coins)"
if y > highscore {
highscore = y
}
highTime.text = "Best time: \(highscore)"
startOut.center.y = 289
coinsLabel.center.y = 130
buyShieldOut.center.y = 167
moveDown.invalidate()
explosion.center = player.center
timer = 0
}
}
This works fine. But I have commented out the time.text line as when it is active the falling objects repeatedly go back to the top of the screen and begin falling again, then go back to the top of the screen again etc. very quickly - a fraction of a second. It seems to make no sense. Any help would be much appreciated.