1. Open the game directory
2. Open Launch.bat file with text editor
Add Exit command to the end of the text
2.1 There you can delete «start BJHelp\help.html» string if you do not want a guide to start with the game
3. Rename Launch.bat to Launch(1).bat (or to whatever you like .bat)
4. Create a new text file in the game directory and rename it to Launch.bat. Open it with text editor
5. Put the following text here:

@echo off
%comspec% /c start "" /min "D:\SteamLibrary\steamapps\common\Casino Blackjack\Launch(1).bat"
<nul set /p "=Press a key to close Casino Blackjack..."
pause >nul
taskkill /im casinobj.exe /f && exit

Edit a path to the game directory to yours instead of mine
Save the file

Now
6. When you play DO NOT close command shell window which starts with the game app
7. When you want to end a game session, just Alt+tab to command shell window and press a key. The game process will be terminated and you will get correct playtime to your steam profile

The script is not optimal, shell window is not minimized (as i planned). Maybe i return to it later...