I also found out that presumably when port 123 is closed on your local wifi network, the WiFi.getTime() can't reach the NTP server. I still have to test this, by opening port 123.
Edit:
Here's some background info, with link to testing your connection online:
TroubleshootingNTP < Support < Network Time Foundation's NTP Support Wiki.
I still can't reach the NTP server, probably because from this location I'm on a high level security connection with the ISP, which blocks outbound traffic on port 123 (UDP). But I know my MKR1000 works with WiFiRTC on another location, with a different internet connection.