Two minutes, once. Kip is a real iPhone app, installed through Apple's TestFlight.
Kip is invite-only. The person who invited you sends you two things: a TestFlight link (installs the app) and your personal invite code (KIP-XXXX-XXXX). The code is your key; keep it to yourself. Joining as a couple? You each get your own code.
Tap the TestFlight link. If your phone asks, install Apple's free TestFlight app first, then tap the link again and hit Install next to Kip. The green Kip mark lands on your home screen like any other app.
Open the app, type your invite code (dashes and caps don't matter) and your first name, and you're in for good on that phone. A code works exactly once, so spend it in the app, not in a browser.
The app opens with a two-minute tour: connect your calendar, try your first check-in, and see what arrives when. That's it. If you ever get stuck, just tell Kip; it's listening from the first screen.