0 0 1 1 * — once a year, at New Year

Answer

0 0 1 1 * runs once a year, at 00:00 on 1 January. @yearly and @annually mean the same.

At 00:00 on 1 January.

0
Minute (0-59)
At minute 0 (on the hour)
0
Hour (0-23)
Hour 0 (midnight, 00:00–00:59)
1
Day of month (1-31)
The 1st of the month
1
Month (1-12 or JAN-DEC)
January
*
Day of week (0-7 or SUN-SAT (0 and 7 = Sunday))
Every day (no restriction)

0 runs a day on average0.02 a week1 of the next 364 days have a run

Hours of the week (darker = more runs)

The next 52 weeks, one square per day

What to know

A yearly job is the hardest to test: make the script runnable by hand with the date as an argument, and test that, rather than waiting for New Year.

If the server is down at that minute, standard cron does not catch up later. anacron (or systemd's Persistent=true) does.