messagebox in timers

I have an ios app with two timers, timer1 and timer2. I start the first timer in multiple mode.
Inside this timer1 i keep track of how often it is called. If it has been called a specific number of times, say 10, I set the mode of this timer to ‘off’ inside the action of the timer. Then I call a message box, after that I start the second timer. These I call also from thy action event of the timer1.

What I would expect is that after 10 actions of the timer1 I get the message and after having read the message and have pressed OK the second timer starts. Actually the message box just does not wait for me having read the message, It starts right away as if th messagebox was not called (BTW i see the message so it is really called but it doesn’t wait)

I am not sure if this iOS specific. That’s why I submit it to general.
Thanks for any clarification.