Question

A time to sow, a time to reap
But over a life, this time would creep

I was created in 46 B.C.
Brought into being by Caesar's decree

But still the seasons were unimpressed
Man-made and tropical slowly digressed

So good Pope Greg set everything straight
with inspired rules that worked out great

I am grander than my common peers
I come 97 times every 400 years

By following my rules, as widely agreed
We all know what day to plant our seed

What am I?

Answer 1

February 29.

Answer 2

I am a Leap Year.

Details for the curious:

There are actually about 365.2422 days per year according to the "tropical year", the number of earth rotations per orbit of the sun.

Using the ancient 365 day calendar, the first day of spring would drift later by about one day every four years.

Julius Caesar created the Julian Calendar with a leap year every 4 years.

Under this Julian calendar, the first day of spring drifted one day earlier every 128 years.

Pope Gregory XIII created the Gregorian calendar in 1582 A.D.

He modified the leap year schedule to exclude three leap years every 400 years.

Years divisible by 100, but not 400 are NOT leap years. So 1800, 1900, and 2100 are not leap years, while the years 1600, 2000 and 2400 still are.

This reduces the error to one day every 3236 years.