I know how it is to be a game dev on a deadline and have ideas of how to expand on a project, how it can be fixed or added to, etc. So please understand if I mention things you already want to fix or add. I'll also try not to repeat points that other people have made that you have responded to.
1) Having both a controls and options button on the main menu, along with a pause feature in the game itself, was very helpful. Allowing the player to set their own time limit and thus their own pace is also a good idea, it fits into the more gentle aesthetic of the game
2) As silly as it sounds, I assumed from the start I had the mail on hand and the "0/10" in the bottom left means I had currently delivered to 0 of the 10 target houses. I ended up wandering some of the map the first time around, hitting E on different houses, before I saw the post office again and pressing E turned that number into "10/10". Since you even start in front of the building, I'm not sure what to say about my thought process, only that maybe appending "letters in bag" at the end of the /10 would prevent fringe cases like mine. That's probably what the envelope icon is meant to convey, but it was still a little ambiguous on my first run
3) The map isn't too large to make memorising it a problem, if you stick to filling out one side of one street at a time you're normally good to go. It would be more convenient if there were a second post office on the other side of the map that you could replenish your mail at, though, as opposed to running back to the same place each time. Not sure how I would narratively explain the mail you need showing up at that building, but I think it could be handwaved
4) Sometimes the NPC or non-playable cats' pathfinding means they squat in front of houses and refuse to leave, and while it's likely random it still feels a little aggravating
5) Does the game run at a consistent 15fps framerate on most machines? I don't have a frame of reference for everyone else's experience with this game, but the game seemed to run really choppy on my computer
Overall it was a pleasant, mostly relaxing experience and it's not every day I can say I played a game about delivering the post. Outside of the obvious ideas (more maps) I'm not sure what additions or improvements I could suggest. Perhaps a cat-sized van for players who want to further immerse themselves in the role? Or a mouse mode, playing on the same map delivering from a smaller post office to mice villagers, but you're all far shrunk down compared to the cat villagers?