DubDubDown
DubDubDown is a very simple app, which lets you know exactly when the WWDC20 by Apple will be started. Plus, it sends a notification (If you click on the Remind Me button) when the conference is about to start.
This includes a watchOS app, as well as a macOS app.
You can get benifit of the countdown technique or even nothing from this open-source app, I just made this when I was bored.