Recently I discovered a very nice tool on debian-like systems called "leave". It's only purpose is to remind you when you have to leave.
$ date +%H:%M:%S 14:17:29 $ leave +0020 Alarm set for Sat May 2 14:37. (pid 53921)
What we did here was setting the leave reminder in 20 Minutes. You also can set a fix time with
$ leave 15:13Too bad this tool does not exist in the AUR. But I discovered a simple way to use the debian version. Just download the deb file. For example the 64-bit version. Unpackage it and you'll find the compiled binary in ./usr/bin/leave. Just move it to this location and you are ready to use it.