To invite someone the easiest way, send them a link that you generate from
this page:
Then watch that page to see when they accept their invite.
(That page is also reachable from the Contacts
Exporting backups (from the Account
You share even more information such as your picture and name when
you share with your QR code at these links:
Scanning those with your cameras will automatically register people and add them to each other's contact lists.
The following are more detailed manual steps:
1) Have them follow their yellow prompts.
2) Scan their QR, or have them tap on it to copy their info and send it to you.
Then you can add them to your Contacts
3) You can register them at their info page
4) Add yourself to their Contacts
Have them visit TimeSafari.app in a browser, preferably Chrome or Safari, and then look for the "Install" selection which adds this app to their desktop. This enables other things, like the ability to "share" a photo from their device directly to Time Safari, and it makes notifications more reliable.
Enable notifications from the Account page