Spring and autumn equinox occur every year in March (spring equinox) and September (vernal equinox). Equinox is the point where the length of days and nights meet. After the spring equinox, days become longer than nights, but nights shorter than days.
As we can see from the timeanddate.com website, the spring equinox takes place on March 20 and the autumn equinox on September 23.
If we check carefully the local time of day on March 20 or September 23, we will see that at all locations on the globe, this coincides with the specified date. By the way, it can also be checked on this site.
Difference even few days
You need to find sunrises and sunsets - accurate to seconds. Perform day and night conversion in seconds, as it's easier to compare two numbers. You will see that this day is different. For example, in some of the places we tested, day of real, local equinox is March 18th. The difference from the official date of the equinox is 2 days. Sounds incredible? Check it out for yourself!