How can I automatically get the time from the computer into an alarm clock (starts at 00:00 when plugged in)?
There are several ways, and they are covered in the comments above.


The answer to your question. Via Arduino USB to serial interface. and a simple batch file on a windows computer example:

@echo off

set datetimef=%time:~0,2%.%time:~3,2%:%time:~6,2%

echo %datetimef% > COM5


COM5 is used as a example, your serial port can be another number.

The format in the example is hour.minute:second