Молодец! (I assume you speak Russian based on your name…), so cool, well done, and thanks for the share!! Amazing what you accomplished in a month and a half. A big inspiration 
highly suggest you reach out to @Art and get featured.
I love too that you even decided to share out the code-base, so those truly curious can view/ replicate what you did! This is great. You might even want to consider linking to your repo from the App Store. This way you might get other developers to create pull requests (special term in Git, where people ask to add changes to your code-base) to add more features.
My only question, why would someone use your app over the built-in time-zone feature in the Calendar app already? From there, I can select the time zone for each city…
If the meeting was in London (or most other cities…), I can just search for it/ change it there:
It then displays the new time-zone, GMT+1
Regardless, even if it does replicate some features already available, your app is focused on making this more easily handled/ managed 
incredible you already got it on the App Store too!! I’d be curious to know how many students here, end up publishing any apps at all. So you’ve already achieved a big accomplishment (one I’m still striving towards) 
There’s some other pilots on here too that might appreciate your app!! I’ll tag one of them…
Check-out @drclive’s awesome app here
@The_Code_Toad some inspiration for you as well!
Cheers and well done @argenteus!!
-Andrew