I think the concept is great and unique, but naturally it's difficult to learn how to write Morse Code so quickly, heh. After reading the comments, adjusting the timings, and trying again more patiently I was able to do much better than the first time.
Personally I'd like to be able to see the timings on-screen; I think you could use a progress bar that fills as you hold the T key, and it could have markings to show you where the dits and dahs start or end. It's something that might help a first-time player while they get a feel for writing in Morse code. I think there could also be audible feedback after the word timing elapses so you know you can input the next word (in case you are distracted looking elsewhere at the screen). But frankly I don't know if any of that goes against the spirit of Morse Code, heh.
Sometimes the guards can reach the top of the screen and their code goes beyond the screen.
Lastly, I think the catalogue could have a transparency slider so that you can still watch the part of the game area that it covers while it’s open.
The sprites are pretty cute and the music is nice. I'd love to see the content you plan to add.