Ahh damn it, I knew at the time that I should set it up to be multiplayer friendly.
I'll add it to do the todo.
Please post further suggestions and issues: https://github.com/SirHall/handcraft_timer/issues
(I may not always see them quickly here)
The github is going to be a problem for me because I don't have an account there. (and don't plan to do one there either)
Unfortunately, I cannot test on my side whether desyncs continue to occur, as my friend can only come online again on Friday....