The biggest concerns with your project are the enclosure and the USB port/time setting. The enclosure, especially, will drive the bulk of the development cost.
I assume that you're not somehow wedded to 3D printing and you're suggesting that as a potential way to make the enclosure, correct? There are many ways to skin a cat and there are hundreds of electronics enclosure manufacturers making thousands of enclosure types and this is not something I would 3D print. For example, what if we could make everything fit into
this?. Would you be happy with that?
Now, on connecting to a PC and setting the time. It's one thing to build a device that acts as an HID keyboard and sends a command to start up Notepad. It's another to build one that works the same way to set the time and off the top of my head I don't see a way to do this without software that has to be installed on the PC.
Potential alternatives, especially if you will only ever build three devices, are an onboard real time clock that is preset to the current time, so it should be reasonably accurate for about a year or two, or an alternative method of getting the time such as a WiFi interface. But that's harder. Or as I mentioned before, loading an application on the PC that this device connects to and automatically sets the time when it's plugged in.
Feedback on my suggested changes?