Install
Download Tardy-1.0.1.dmg below, open it, and drag Tardy to Applications.
It is signed with a Developer ID and notarized by Apple, and it updates itself
from then on. Tardy watches the calendars in the Mac Calendar app, so add your
accounts there first.
Verify
spctl --assess --type open --context context:primary-signature -vv Tardy-1.0.1.dmg
shasum -a 256 Tardy-1.0.1.dmg
# d879909d181fe0dfbc5411be50798339cd38a1be9e3621deab262d5d0fe58675