Since the world bosses are on a fixed timer now, I converted this table:
https://www.guildwars2.com/en/news/the-megaserver-system-world-bosses-and-events/
into an .ics file that you can import into your phone calendar or similar programs. I have not tested it outside my own timezone (Europe/Berlin), though I included time zone info in the file.
Get it here: https://alanceil.pegasus.uberspace.de/code/gw2/gw2-worldbosses.ics
Here’s the source shellscript in case you need to change something around:
https://alanceil.pegasus.uberspace.de/code/gw2/gw2-worldbosses-src.tar.bz2