Depends on your use of it and communication of it.
Weeks are based around quarters of the lunar cycle. Twenty-eight (well… Technically 29 and some change) days for a full lunar cycle. Years are pretty obvious.
Longer periods of time tracked the pattern of the planet Venus or other stars.
The longest one we track is the precession of the sunrise against the constellations on the vernal equinox - which is about 24,000 years long.
These calendars are "perfect." They can predict eclipses and other such things with extreme accuracy.
Theybare just cumbersome to use for business and social planning. Thus - we have standard calendars.
The lunar new year is different from the solar new year, as well. The solar new year falls on the apogee of Earth's orbit, or the Perigee if you're using the southern hemisphere's shorter winter as your marker.