Why I cannot change the value of variable inside Timer.scheduledTimer function?

When I try to change the value of accumulatedTime inside Timer function, the value of accumulatedTime retains unchanged.

import UIKit

class WelcomeViewController: UIViewController {

    @IBOutlet weak var titleLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
        titleLabel.text = ""
        var accumulatedTime = 0.0
        let logo = "Hello World"
        for letter in logo {
            Timer.scheduledTimer(withTimeInterval: accumulatedTime*0.1, repeats: false) { (timer) in
                self.titleLabel.text?.append(letter)
                accumulatedTime += 1  // increase the value of variable inside block function
            }
            print(accumulatedTime)
        }
    }
}

// Output is 0.0, 0.0, 0.0, 0.0, 0.0, 0.0...

But if I move the "accumulatedTime += 1" outside the block function of Timer.scheduledTimer, the value of accumulatedTime can be changed again.

import UIKit

class WelcomeViewController: UIViewController {

    @IBOutlet weak var titleLabel: UILabel!

    override func viewDidLoad() {
        super.viewDidLoad()
        titleLabel.text = ""
        var accumulatedTime = 0.0
        let logo = "Hello World"
        for letter in logo {
            Timer.scheduledTimer(withTimeInterval: accumulatedTime*0.1, repeats: false) { (timer) in
                self.titleLabel.text?.append(letter)
            }
            accumulatedTime += 1 // increase the value of variable outside block function
            print(accumulatedTime)
        }
    }
}

// Output is 1.0, 2.0, 3.0, 4.0, 5.0...

I am curious why I cannot change the value of local variable inside the block function of Timer.scheduledTimer, Can you guys help me to understand the inside logic of this.. Thank you

for letter in logo {
            Timer.scheduledTimer(withTimeInterval: accumulatedTime*0.1, repeats: false) { (timer) in
                self.titleLabel.text?.append(letter)
                accumulatedTime += 1  // increase the value of variable inside block function
            }
            print(accumulatedTime)
        }

Print statement runs before closure execute ... thats why they are all 0 .. because its not get SET when your print code execute in for loop ... take print statement inside closure

for letter in logo {
                Timer.scheduledTimer(withTimeInterval: accumulatedTime*0.1, repeats: false) { (timer) in
                    self.titleLabel.text?.append(letter)
                    accumulatedTime += 1  // increase the value of variable inside block function
                    print(accumulatedTime)// print 1,2,3 .. 11
                }

            }

in Closure its value is changing ... and you can access changed value when closure execute ..