Updated June 5th, 2019.
Add the knock-out stage FIFA World Cup 2018 schedule to your Mac’s Calendar by visiting this link. Choose the “Subscribe” option and the calendar will update as the tournament progresses, and add the calendar to “Location: iCloud” (rather than “Location: On My Mac”) if you want the calendar to also show up on your iPhone and iPad. Of course you can simply add the calendar to your iPhone or iPad directly, using the link. Note: I made this calendar myself and will update it as soon as I get the results of the matches.